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[Assistant] Even our phones tell us more than just where the sculpture park is.


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[Assistant] Once we know where things are in space, we can understand how they're related, or their spatial relationships. In fact, humans are hardwired to think about spatial relationships and how we're related to the space container around us. To describe those spatial relationships, we need to recognize topological space, which measures and analyzes how the features in space are arranged and connect to each other. This term comes from the word topology.


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[Assistant] Photogrammetrists and other remote sensing professionals compile and analyze images from satellites, airplanes, or drones that have sensors that record energy reflected from the Earth's surface. The reflected energy is sensed by a device that records the wavelength as a number and turns that number into a pixel in an image. Remote sensing has been particularly helpful in Antarctica, which is incredibly hard to study in person.


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[Assistant] Covered in ice and snow, this frigid continent has been one of the least mapped areas on Earth. And for good reason.


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[Assistant] Conditions are so extreme that hiking around and recording the terrain in a ground-based mapping effort is nearly impossible. So in 1997, researchers collaborated with NASA and the Canadian Space Agency to use remote sensing satellites with radar capabilities known as RadarSat to scan the surface of Antarctica.


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[Assistant] They generated accurate images of the surface ice and snow on Antarctica by measuring the echo of radio waves sent from a radar satellite. With this data, we can start by defining the boundaries of features in Antarctica, like the location of large cracks in the ice called crevasses. We're defining the space, or container, that is this polar continent. But definitions of any kind are really just the initial building blocks.


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[Assistant] In Antarctica, we can use that information to analyze our relationship to those features. Cravasse zones are dangerous to cross and difficult to see from the ground, so knowing where they're located can help create safe travel routes. This can save time and lives when trying to navigate this dangerous terrain.


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[Assistant] But our spatial relationships are more than just routes. The radar dataset is also used to measure how quickly glaciers are moving, which gives us insight into the physics of glaciers and lets us better predict how glaciers change. We can build a more complex understanding of a space when we ask not just, where is the crevasse, but how is it changing? Or,


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[Assistant] Where is that ice moving? Now, containers and topology are informative, but they don't let us talk about the more subjective things we know about a space. In geography, we can also talk about socially constructed spaces, or those spaces we create and give meaning to as communities, like that coffee shop or sculpture park. In fact, the socially constructed space doesn't even have to be physical.


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[Assistant] The way we develop and define virtual spaces, like the fan communities we form and participate in online.


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[Assistant] Each January, blocks of ice from the Songhua River that flows through the city are carved into sparkling sculptures as a part of the annual Harbin International Ice and Snow Sculpture Festival. Originally, ice lanterns were mostly used at night on the river by fishermen. They gradually became an art form and, eventually, a major social and cultural event. Now, the wonder of the Ice and Snow Festival is synonymous with Harbin.


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[Assistant] By studying socially constructed spaces, we learn how space is carved out and a place, or a location with meaning, is created and can become sites for social, political, or economic activity. Individuals, not just communities, can also create meaning in space.


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[Assistant] We study individually perceived space to incorporate the idea of place and see how the perception of a space can change person to person or culture to culture. Like a teenage girl living in Harbin might hold a mental map of her neighborhood that includes points of interest to her, like the curb she almost twisted her ankle on while jogging.


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[Assistant] That's her perception of that space, just like we all have our own perceptions of our individual spaces. And we can see how the perception of individuals or groups has changed over time. Today, Harbin is the eighth largest city in China.


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[Assistant] But its name was originally a Manchu word meaning a place for drying fishing nets, which hints at how past inhabitants perceived and used the space. Any space can be studied through any of these four lenses, as a container, topologically, socially, or how we individually perceive it. Let's go to the Thought Bubble.


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[Assistant] In January 2010, a magnitude 7.0 earthquake shook the nations of Haiti and the Dominican Republic, creating massive damage and killing hundreds of thousands of people. But things could still get worse. Relief efforts in Haiti were delayed because aid workers didn't know where to go or how to get there.


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[Assistant] Clear maps of neighborhoods and remote regions of the island before the quake just didn't exist, so international aid workers had no sense of space and no fast way of learning. But the locals did know the area.


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[Assistant] What was there, how it was organized and what it meant for their communities. So that collective knowledge or perceived space was put to work.


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[Assistant] In two weeks, Haiti went from no map to a complete map in the first crowdsourced mapping effort for humanitarian purposes. A team of mappers organized people around the world to help digitize photos, which means tracing images to create 2D shapes and attaching coordinates that can be plotted on a map. These humanitarians input aerial and satellite images into a mapping platform called OpenStreetMap.


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[Assistant] With OpenStreetMap, volunteers can look at space as a container and use those images to trace buildings, parks, roads, and more to create a basic digital map.


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[Assistant] That map can then be used by anyone in the world with access to open street map. In Haiti, those maps meant relief workers could see where buildings should be and could use that to help identify where people might be trapped.


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[Assistant] Since 2010, communities around the world have worked with an open street map digitizing their buildings, roads, and other features. Local citizens imbue the map with meaning, like which of these buildings are houses, or where there are important community gathering places, hospitals, and businesses. Local groups and humanitarians can then create the maps they need to achieve their goals, from identifying areas at risk for disease spread,


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[Assistant] To identifying safe areas for persecuted groups, to helping locate people quickly after a natural disaster. Because anyone can update the map as spatial features change.


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[Assistant] We navigate space every day, rely on fresh geographic data to get from place to place, or give meaning to familiar and unfamiliar spaces without much thought.


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[Assistant] As geographers, we formalize that process. We take in spatial data from satellites, photos, radar, and personal observation and create data that allow us to locate buildings, route around traffic or physical features efficiently, and communicate the meaning communities give their spaces.


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[Assistant] We focus on space explicitly to better understand and explain the world around us.


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[Assistant] Many geographical place names also don't reflect the indigenous or aboriginal people's languages. So we at Crash Course want to acknowledge these people's traditional and ongoing relationship with that land and all the physical and human geographical elements of it. We encourage you to learn about the history of the place you call home through resources like nativelands.ca and by engaging with your local indigenous and aboriginal nations through the websites and resources they provide.


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[Assistant] If you'd like to help keep Crash Course free for everyone forever, please consider joining our community on Patreon.


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[Assistant] Sloth wants to snooze. Written by Russ Ulyak.


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[Assistant] Illustrated by Sherilyn Barnes.


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[Assistant] She climbed into the vines. The monkeys were too noisy.


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[Assistant] The big cats were too noisy.


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[Assistant] The rainforest is too noisy. I can't sleep, she told the bat. You're so tired, you forgot.


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[Assistant] Swalts can sleep anywhere. Set the bat.


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[Assistant] Sloth smiled. She closed her eyes. And snoozed at last.


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[Assistant] From espressos and cappuccinos to cafe au lait in plain black, there's a coffee out there for almost everyone. We can even visualize it on a map like this, where the color of each country represents how much coffee they drink per person.


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[Assistant] But for coffee to get to my favorite coffee shop, it first has to make it through a pretty long journey. We won't go bananas and get into the full geographic story of coffee, but in 2020, coffee is mostly grown in the beanbelt. Which is… oh, I'll just show you. My favorite coffee shop is much closer, though, over on Elm Street.


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[Assistant] Walk past there, take a right at the next corner, and the cafe is straight ahead. At least that's the mental map I follow every morning. We all have maps we use as tools to help us navigate or better understand where we are. And in geography, we use maps to study, analyze, and interpret spaces, places, and human-environment interactions. We use maps in all shapes and sizes to tell the story of the Earth.


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[Assistant] They're colorful, detailed, and lots of times, difficult to fold. I'm Alizé Carrère, and this is Crash Course Geography.


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[Assistant] Maps can be used to compare spaces and places on Earth and beyond, or shape our sense of reality. Like, when you search map on the internet, this world map is one of the first that comes up.


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[Assistant] So this reference map also has to do the hard work of representing our three-dimensional world in just two dimensions. Like taking the 3D Earth and squishing it onto paper or a flat computer screen. Imagine doing that with a tomato.


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[Assistant] What a mess. For cartographers, or mapmakers, it's a challenge with many solutions. They need to pick which data they want to focus on, and the type of map they pick often depends on what story they want to tell.


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[Assistant] For example, we might want to use these three maps to talk about the number of people in each country around the world. They're thematic maps, which visualize data about a particular topic across a space. Instead of being something we'd use to navigate on a cross-country road trip,


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[Assistant] Thematic maps tackle abstract ideas, like average rainfall or voting results by political party, and explore how frequency, concentration, and patterns are distributed across a space. For example, these three thematic maps are designed to visualize population data.


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[Assistant] First we have a chloropleth map, which shows how a theme like population changes over a particular space using different colors or shadings of colors. This is shown in the map's key, or legend, which unlocks the map and shows us how to get into the map and interpret it. Notice how the key moves from a light purple to a deep violet.


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[Assistant] Except for the northern tip of the continent, there are between 0 and 25 people per square kilometer. But wait!


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[Assistant] As of 2020, São Paulo and Brazil is actually one of the 20 most populated cities in the world.


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[Assistant] Nowhere? Chloropleth maps are useful because they quickly tell us which countries or regions belong in the same category overall. With a glance, we see Australia and Canada and Russia and most of South America all fit in the same population density category. But by shading a whole area, chloropleth maps can make things look a little too simple, which can be a problem.


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[Assistant] They imply there's an evenness to whatever they're showing, even though there are parts of Sao Paulo with way more than 25 people per square kilometer, and other parts of Brazil with absolutely no people. Let's try a different thematic map that will let us be a bit more specific.


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[Assistant] A dot density map uses a dot to represent a key feature or attribute. The cartographer decided that each dot on this map represents 100,000 people.


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[Assistant] So while the chloroplast map showed the general population spread out over an entire country,


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[Assistant] This dot density map has more granularity and shows where, within a country, people live. More or less. We can see the coasts of Brazil have more dots, and more people. But take a look at the Sahara or Siberia.


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[Assistant] No one lives exactly where those dots are. The cartographer also decided where to place each dot to summarize population data. But it's a simplification that could mislead someone if they're not paying close attention, like we are.


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[Assistant] A dot doesn't necessarily mean 100,000 people live exactly there. Cartographers are always trying to make maps easily readable, but all the choices they make can influence accuracy. For example, if we changed how our dot density map is projected, or how the 3D Earth was flattened into 2D,


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[Assistant] We might accidentally imply some areas have a closer population density while others are more spread out. Our last thematic map for today is a cartogram map, which uses size to compare data, like population density.


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[Assistant] Regardless of the actual space, these regions take up on the Earth's surface. With this map, the really populous countries are giant. Well, ones with smaller populations are teeny. But it looks weird to us, or at least to me, because we're used to maps that tell us something about the physical space that countries and continents take up. India has a much bigger population, but in real life, Australia is a much larger country.


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[Assistant] It's about 7.7 million square kilometers, while India is less than half the size, with 3.28 million square kilometers. Each of these thematic maps uses a different lens to tell the story of the world population.


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[Assistant] Different maps represent data in different ways, and the more information a geographer has, the better interpretations they can make about a particular story.


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[Assistant] And those choices, however thoughtful or simple or unintentionally biased, have an impact on how we imagine the world. Like, we're so used to seeing north at the top of a map and south at the bottom. But why?


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[Assistant] We can spot these obvious or not-so-obvious choices made by cartographers. For centuries, humans have been using maps as navigational tools to help us understand our physical surroundings.


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[Assistant] Mariners had their own stick charts that they used to get back to the places they'd visited. Kinda like my mental map to my favorite coffee shop.


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[Assistant] There's a dispute over territory in Antarctica and some nearby islands that's currently on pause thanks to a 1959 treaty. Originally, the 12 countries whose scientists had been conducting research on the continent signed and agreed that no activities taking place would mean they'd claimed the territory.


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[Assistant] But in the 1960s, despite the treaty, Argentina published maps claiming territory in Antarctica.


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[Assistant] Let's say it's the 1950s, and we're US cartographers working on a new world map. The Cold War between the United States and the Soviet Union is nearing its height, and the tension can influence our map-making decisions. First, we have to choose a kind of projection, like the Mercator Projection.


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[Assistant] First made in 1569 by the Flemish cartographer Gerardus Mercator.


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[Assistant] This type of map basically turns the spheroid Earth into a cylinder. The Mercator projection shows the lines of longitude, or meridians, as equally spaced and parallel vertical lines traversing pole to pole.


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[Assistant] The lines of latitude, or parallels, are also parallel lines on this map. But get spaced farther apart as we move north or south of the equator. On a globe, meridians aren't equally spaced, but curved together at the poles. With this layout, the scale gets distorted and areas farther away from the equator appear bigger than they really are. Like look at Greenland.


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[Assistant] It's essentially the same size as all of Africa. It's not that this representation is wrong.


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[Assistant] Every map choice comes with its flaws. But by choosing a Mercator projection, the USSR looks large and menacing. That's just the beginning, so we sketch out country borders. And now it's time to add color.


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[Assistant] Though the Cold War is over, our maps still reflect nationalistic fervor in more modern times.


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[Assistant] We like to think of data and numbers as being objective, but how data is displayed on maps can affect what people believe about the world. Like, these two maps both show the Hispanic population in Florida, based on the 2000 census. They look like very different maps, but it's actually the same data.


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[Assistant] Maps can even be used to tell stories about societal problems. On this map, major chemical accidents, environmental disasters, freak weather patterns, and deforestation are all included with different symbols.


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[Assistant] So looking at this map might make you feel like the Earth experienced great environmental stress in the 1980s and 1990s. And that's a choice the cartographer made. Maps can make strong arguments because they pull a lot of visual information together, which can increase our awareness about certain issues, or greatly skew our understanding of the world. Maps are powerful tools, and they'll be a crucial part of our journey through geography.


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[Assistant] Many geographical place names also don't reflect the indigenous or aboriginal people's languages. So we at Crash Course want to acknowledge these people's traditional and ongoing relationship with that land and all the physical and human geographical elements of it. We encourage you to learn about the history of the place you call home through resources like nativelands.ca and by engaging with your local indigenous and aboriginal nations through the websites and resources they provide.


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[Assistant] Thanks for watching this episode of Crash Course Geography, which was made with the help of all these nice people.


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[Assistant] If you'd like to help keep Crash Course free for everyone, forever, please consider joining our community on Patreon.


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[Assistant] A flowing moon temple. A sanctuary of peace.


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[Assistant] Hi, welcome back. We're in lecture one, segment two.


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[Assistant] We're talking about experimental research. In the first segment we talked about the polio vaccine trials.


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[Assistant] The jury's still out as to whether this type of experimental research is as successful as the polio vaccine trials. So I'll describe one experiment to you to give you a flavor for how this works and we'll talk about why there's still some controversy around this research.


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[Assistant] So, the idea behind memory training, and you may have seen some of these things online, uh, referred to as brain games, uh, that you can train your memory, train your attention to enhance your intelligence.


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[Assistant] Uh, is you, you engage in days and days and days, perhaps weeks up to a month of memory training and you do a


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[Assistant] Test before, a test after training, that's called a pre-post-test design.


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[Assistant] You can do experimental research to answer this question. So I'm using the, the, uh, my sort of basic lingo from last segment. We could promote good stuff. So if we know why this happens, why we can, uh, enhance memory and intelligence, perhaps we could promote good stuff by, uh, by doing this memory training research.


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[Assistant] So the way an experiment works to get at memory training.


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[Assistant] Brain training games or memory training games focused at children. Uh, what I'm gonna talk about today in this, in this lecture are just some, uh, experiments designed for healthy adults.


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[Assistant] So our sample and the sample from the experiment that I'm going to talk about is just a sample of college students.


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[Assistant] Exactly a random representative sample of all healthy adults. Uh, college students aren't, uh, they're not random, they're not completely representative. Uh, but that's typically how research is done because we have, we can get our hands on them here on a college campus.


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[Assistant] The way these experiments are set up is the independent variable is the training condition. So whether you go through some sort of memory training.


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[Assistant] Or whether you don't. And this is an interesting aspect of these training experiments. Uhm, what I'm gonna describe to you in this first example is a no training control group where the control group just did nothing.


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[Assistant] So there's memory training versus nothing. Uh, there's other ways to do this that are, uh, sort of stronger tests of this claim that memory training enhances intelligence. Uhm, but for now we'll just keep it simple.


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[Assistant] The dependent variable is the gain on an IQ test.


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[Assistant] So as I mentioned, subjects in these experiments, they take an IQ test before training, and then they take an IQ test after training. And we can look at the difference to see how much does an individual subject's IQ increase as a function of training. So the dependent variable here is IQ gain. The idea being that subjects in the training condition


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[Assistant] Their IQ is going to increase more so than subjects who are assigned to the no training conditions.


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[Assistant] So the procedure in this one experiment that I'll describe to you is the treatment group, the, the memory training group. They engage in memory training for half an hour a day, every day for weeks. I think it was up to like four weeks, four or five weeks.


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[Assistant] And I'll show you the training procedure on the next slide. Uh, and as mentioned, they, they took an IQ test, a reliable standard measure of IQ, uhm, before and after training.


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[Assistant] Now here's what the memory training paradigm look like if you're not familiar with, uh, the idea of working memory or short-term memory. This may look a little odd to you, so let me take some time to explain it. This task is called a two-back task.


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[Assistant] Uhm, and very simply what you're supposed to do as, uh, the student in this task, uh, or someone who's engaging in this training paradigm, is you're gonna see stimuli pop up on the screen or you're gonna hear stimuli presented over, uh, headphones.


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[Assistant] So you're going to see either locations, squares, excuse me, squares show up in different locations on a screen or you're going to hear letters


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[Assistant] That is a visual target because it's in the same location as the stimulus two back in the stream.


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[Assistant] Similarly, in the auditory stream, this one is an auditory target because it matches the one two back in the stream.


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[Assistant] In this case, this is known as a dual end back procedure. The subject was supposed to press the button only when the stimulus matched in both the visual and auditory stream. So again, this right here.


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[Assistant] Is when the subject would press the button saying, yes, this stimulus matches the one, two back.


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[Assistant] As I mentioned, subjects in the memory training condition, they engaged in this for this training procedure for half an hour a day, every day.


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[Assistant] Up to 19, you can see 19 sessions down here on the x-axis. So what I'm plotting here on this graph is on the x-axis is session number. So how many training sessions did they engage in?


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[Assistant] And what I'm plotting on the y-axis is the mean and back score.


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[Assistant] So, as you can see, people started out down here around three back.


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[Assistant] And as they engaged in training over 19 sessions, 19 days of doing this for a half an hour a day, they got better and better and better, up to about 5 back, some people probably got as high as 6 back, okay.


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[Assistant] If you've done this task before, if you have any familiarity with some of these brain


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[Assistant] Uhm, the jury is still out as to exactly what they're training. Uh, so some people argue they're training a core memory capacity that's related to intelligence. Uhm, other people would argue that uhm, they're training, uh, they're just getting faster at doing tasks online or something else.


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[Assistant] But these are some of the basic results from, uh, this study.


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[Assistant] The bigger question is whether there was transfer to intelligence. So people clearly get better at the task that they're training in as they do the training procedure every day.


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[Assistant] Uh, the bigger question is whether those people in the training condition got better on the intelligence test relative to a control group that didn't do the training.


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[Assistant] And here are the results uhm, from a study by Yaki et al. The reference is here. Uh, if you want to look it up, it's Yaki et al. 2008. Here is the primary result from that study that caused a lot of buzz and, and generated a lot of attention uhm, in this area of research.


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[Assistant] Is if you look before the training, so what I'm plotting here on the x axis is pre and post. So this is just time. So before training.


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[Assistant] There's no difference between the experimental group and the control group. That is, between the memory training group and the true, the placebo group, if you will. The group that did no training. There's no difference in their intelligence score. So what I'm plotting here is their score on an intelligence test.


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[Assistant] But what you see after training, so post training, the group that did


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[Assistant] The memory training procedure, they gained more on the IQ test than did the group that didn't do the training, the control group.


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[Assistant] The control group went up a little. That's probably just a practice effect. They took this intelligence test before. This is their second time taking it. So there's a little bit of a practice effect. But the bigger point is this difference here.


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[Assistant] The group that did the training gained more than the group that didn't do the training.


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[Assistant] So the conclusion from this experiment then is engaging in this memory training procedure, doing this end back task for a half an hour every day for 19 sessions not only enhances your ability to do that end back task or enhances your memory capacity,


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[Assistant] But it also, according to these authors, enhances your basic intelligence, your general intelligence.


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[Assistant] Uh, because the conventional wisdom in those fields is that intelligence and sort of memory capacity are sort of fixed once you get to adulthood. They're very hard to, it's very hard to change, uh, your level, uh, IQ.


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[Assistant] As I said, the jury is still out on a lot of this work. So I said here, does it really work?


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[Assistant] Uhm, there are lots of people who argue that this does not work and this is, this is a fluke result.


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[Assistant] Yaki et al have followed up on this research and argued no, that this result is real and that you can engage in these memory training tasks to enhance uh, intelligence.


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[Assistant] Uhm, my perspective on this, I do research in this area, I study working memory and intelligence, is I would argue so far, there's not enough evidence to suggest that these things really work. So if I were you, I would not go out to these websites and spend any money on these things, not just yet.


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[Assistant] Uh, I think we need more experimental research, uh, to get at, uhm,


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[Assistant] To see if the, if these results are, are really strong and if we can replicate them, uh, with different kinds of memory training paradigms and most importantly with better control groups. So in this example, the control group did nothing. So that's a really poor control group.


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[Assistant] So when you do experimental research, you really want the difference between the experimental group and the control group to be as small as possible so that you can make that causal claim about why the outcome happened. You can, you can link it to


[User] Please transcribe this text

[Assistant] The, that small difference between the experimental group and the control group.


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[Assistant] The experimental group came to this lab every day for 19 days. They got better on a task that they were doing on the computer every day, so it was rewarding. They felt better about themselves. They had maybe just a more positive feeling about this lab, about


[User] Please transcribe this text

[Assistant] Cognitive tasks in general, so when they came back for the post-test on the IQ, they could have just done better because they felt better about themselves.


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[Assistant] Uhm, they could have felt better in that environment. Uhm, there's all sorts of reasons why this result could have happened. Uhm, that has nothing to do with memory training per se or IQ per se.


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[Assistant] Uhm, and if you're interested in this uhm, line of research, uhm,


[User] Please transcribe this text

[Assistant] Again, Google, you can just Google working memory training. Uhm, there's lots and lots of studies now on that, on that topic. Again, I would argue that the evidence isn't strong enough.


[User] Please transcribe this text

[Assistant] Uhm, to claim that this really works. Uhm, clearly it doesn't work like the polio vaccine worked. Alright, so this is an example of experimental research that's not quite as good as, as those polio vaccine studies.


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[Assistant] Not, uh, not sort of high quality experimental research. Lots of potential confounds.


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[Assistant] Okay, so to summarize, this is the same summary from segment one.


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[Assistant] The major benefit of randomized controlled experiments is that they allow for strong claims about causality. They allow us to get at mechanism why things happen.


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[Assistant] Uhm, again, we can predict stuff that allows us to prevent bad stuff like polio.


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[Assistant] And potentially allows us to promote good stuff, like intelligence. If we could use working memory training to enhance intelligence, then great. That's a great idea. I think everybody's behind that idea. Uhm, but not everybody believes that it really works so far. And I'm, I'm still, uh, pretty skeptical myself.


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[Assistant] And again, that's because we need really good independent variables, random and representative samples. Again, that was another problem with that study. It wasn't truly a random representative sample of all young adults, right? It was college students.


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[Assistant] Uhm, and we need no confounds and there are lots of potential confounds. I, I, I encourage you to, to post on the discussion forums your own ideas, uh, of the potential confounds in, in this line of research.


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[Assistant] Uhm, there's lots and lots of, uh, confounds that I didn't mention here, but you could mention in the discussion forums if you like.


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[Assistant] Uhm, so this is an example where uhm, it's true experimental research. It's true that those subjects came to the lab. They were randomly assigned to do either training or no training. And they were assessed on some dependent measure. So it's a nice example of a randomized controlled experiment.


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[Assistant] But it's an example of an experiment that's not, that doesn't allow for strong causal claims yet because of all these potential confounds, unlike the polio vaccine example.


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[Assistant] You must forgive me. But there is much fear in our little village.


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[Assistant] I wasn't able to arrest him We need more help


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[Assistant] Journey to the West, Chapter 70, The Star Lord.


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[Assistant] A little while later, Wukong stood at the southern gate of heaven.


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[Assistant] The guard told Wukong the way to the Star Lord's palace.


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[Assistant] A few minutes later, the monkey knocked on the palace door.


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[Assistant] Wukong led the Star Lord out of heaven and down to earth.


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[Assistant] They landed on the mountain, where Bajie was still rubbing his nose.


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[Assistant] Said Wukong. The Star Lord looked at Bajie's nose.


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[Assistant] Bajie walked over to the Star Lord, who then blew on the pig's nose. The injury healed instantly.


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[Assistant] Wukong stood in front of the cave entrance and shouted.


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[Assistant] Then he ran as fast as he could away from the cave.


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[Assistant] The woman rushed out of the cave, spinning wildly.


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[Assistant] Suddenly the Star Lord turned into an enormous rooster.


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[Assistant] I dreamt I was given this tablet by the king of Wu Ji. And when I awoke, there it was. I must give it to his son. He will pass by here tomorrow.


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[Assistant] Journey to the West, Chapter 67, The Master Thief.


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[Assistant] The warrior rubbed his chin. He looked very serious.


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[Assistant] Now everyone looked at Wukong. The monkey pretended to laugh.


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[Assistant] He went down a long dark tunnel followed by another tunnel.


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[Assistant] Then he heard one horned buffalo. Wukong flew toward the voice.


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[Assistant] The demon was sitting on the edge of a bed, talking to himself. The metal ring was still on his arm.


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[Assistant] He made his iron bar small and put it in his ear.


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[Assistant] Then he grabbed the flaming spear, the thunderbolt, and the sword. Outside the cave, the others were waiting. The warrior made a fist.


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[Assistant] When they saw Wukong peek out, they were relieved.


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[Assistant] Ask the thunder god. No, but look! The monkey held up the weapons.


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[Assistant] Said the fire god. The thunder god clapped the monkey on the back.


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[Assistant] The warrior held up his sword.


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[Assistant] You're right, said Wukong. He looked around.


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[Assistant] It is hot. Maybe we should take a break.


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[Assistant] All the land around the mountain is covered in flames! The land stretches far to the north and the south! It's impossible to go around!


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[Assistant] She has a special fan that can put out the flames. It's made from a plantain leaf.


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[Assistant] Hey kids, now we're going to write the letter J, as in Jaguar. J, J, Jaguar.


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[Assistant] First we'll write the capital J. That's the big J. Start at the top.


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[Assistant] And go down to the bottom, then go around and up.


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[Assistant] Next, go back to the top and make a line across.


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[Assistant] Let's try it again. Down, around and up.


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[Assistant] Start in the middle and go down below the bottom, then go around and up.


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[Assistant] Next, make a small dot above the middle.


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[Assistant] Let's try it again. Down, around, and up. Make a small dot above the middle. Now you try.


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[Assistant] Next time, we'll write the letter K. Don't forget to subscribe to our YouTube channel.


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[Assistant] I am so tired. So many miles have I traveled on these weary legs. We shall help you. Try and stand up. Oh, good monk. I can no longer stand or walk, for I have come through these mountains on foot and amorn out.


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[Assistant] Spreading across the Pacific Ocean, the North Pacific Garbage Patch is really more of a series of trash vortices and is the top vacation destination for plastic, chemical sludge, and wood pulp. Defining its size is difficult because it's always moving and it's mostly a soup of tiny microplastics, not an island of grocery bags and drinking straws.


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[Assistant] Actually, it's one of five giant collections of trash circulating in oceans all over the Earth. If you've spent time on beaches, you might have noticed plastic trash like water bottles and toys, but there's so much almost-invisible junk too, like small beads or tiny slivers.


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[Assistant] Each beach around the world has this plastic pollution because of how trash moves from inland to the ocean, and then gets caught in ocean currents. Whether you live on a coast or not, everyone is connected to global ocean currents circulating tremendous amounts of energy.


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[Assistant] To get there, it all starts with the wind. In our last episode we explored how the horizontal movement of air, called wind, moves in predictable directions and creates the general patterns for global circulation.


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[Assistant] Because of how much direct sunlight it gets, water closer to the equator absorbs more heat energy than water at higher latitudes. This creates density differences within the ocean, because, just like air, warm water is less dense than cold water. Basically, when heated, molecules like to spread out.


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[Assistant] Water density is also affected by salinity, or the salt content of the water. Saltier water is more dense than less salty water because there are more molecules of salt and water hanging around. Warmer water in the ocean expands just like air, but because it can't expand sideways, because you know there's already water there, it expands up, elevating the surface just slightly, like a hill.


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[Assistant] And in general, whatever's in a high pressure area, whether it's air or water or a student in a stressful class, wants to move to a low pressure area.


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[Assistant] So if our trash found its way to the right spot, it could travel the world. We can draw lots of comparisons between ocean currents and wind patterns, but surface currents are also driven by strong and steady streams of wind.


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[Assistant] Energy is transferred from the winds to the water through friction as air blows across the surface. For example, the winds that result from subtropical high-pressure areas around 30 degrees latitude also help create the ocean currents that circulate there in patterns called gyres. But even though ocean currents generally follow the winds, the two aren't mirror images.


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[Assistant] Remember, the Earth is rotating fastest at the equator and slower as we move towards the poles. So if something that's not directly connected to land moves north or south, the change in momentum causes its path to bend. The Coriolis effect can actually deflect some surface currents, depending on where they are on the globe.


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[Assistant] Like, as currents move away from the equator, the Coriolis effect gets stronger because the Earth's rotational speed rapidly slows down, and can break up currents into chains of lots of circular vortices, or eddies.


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[Assistant] These get smaller the closer you are to the poles as the Coriolis Effect bends the currents ever more tightly. Then, as the Earth rotates faster as we move towards the equator, the Coriolis Effect gets weakest until it's basically non-existent exactly at the equator.


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[Assistant] So equatorial currents aren't deflected right or left. Water can simply flow in a straight direction, pushed by the winds. So if we look at the circulation map, most of the surface currents making up gyres don't cross the equator, but flow along it horizontally.


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[Assistant] You know, if water bottles had arms. As it reaches the latitude of the westerly winds around 35 degrees north, the current begins to wobble more, and along with our bottle, is pushed eastward and separates from the coast. This forms the North Pacific Current, bringing warm waters to the southern coast of Alaska. And then, land ho!


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[Assistant] Eventually, our water bottle encounters the west coast of North America and is deflected back towards the equator, moving from British Columbia, Canada to the Baja Peninsula in Mexico.


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[Assistant] There are actually five major gyres in the world, including this North Pacific gyre, each with its own garbage patch. And they all follow similar patterns, with warm currents bringing warmth and humidity to the continental east coasts, and cold currents moderating temperatures and having a drying effect on the west coasts. Ocean circulation in the southern hemisphere is similar, except that the gyres flow in a counter-clockwise direction. And because there's very little land poleward of 40 degrees south, the Antarctic Circumpolar Current, or West Wind Drift,


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[Assistant] Circles around Antarctica as a cold current, almost without interruption or directly interacting with the warm equatorial waters. Surface currents generally move warm waters poleward and cold waters toward the equator, so they're important regional air temperature regulators in addition to moving anything that happens to be in the ocean, from schools of fish to bits of plastic.


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[Assistant] To see the rest, we have to go deep into the ocean. Deep currents travel at slower speeds beneath the surface currents. They move ocean waters both horizontally across the floors of the world's oceans, but also vertically from the ocean floor to the bottom of surface currents as part of Earth's thermohaline circulation. Just like surface currents, deep currents flow from high pressure to low pressure.


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[Assistant] Even at these crushing depths, slight pressure and density differences are also caused by temperature and salinity changes. For example, the more salt content the surface water has, the more dense it is, the more likely it will sink as it reaches the poles. In some places, that water will sink up to 2000 meters to where deep currents flow.


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[Assistant] A complete circuit of a deep current may take up to 1000 years. Even still, deep currents are critical to the movement of nutrients around the world. Many fisheries, for example, depend on cyclical upwelling of nutrient-rich water moving from deep currents into local surface currents. While nutrients released through decomposition near the ocean floor are pulled up by upwelling, oxygen cycles down from the surface to the deep.


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[Assistant] So the broad global circulation of deep currents is like a vast conveyor belt of ocean water that brings warmth from the equator to the poles, nutrients from the floor to the surface, and oxygen from the surface to the floor. Marine habitats near upwellings only cover about 1% of Earth's oceans, but account for up to 50% of the global fish harvest.


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[Assistant] At least a billion people rely on fish for their primary protein, so deep ocean circulation not only moves energy around the globe, but also helps create the conditions that feed a large part of the world.


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[Assistant] Further up, dominant winds and surface currents have helped move people around the globe for thousands of years. With the movement of ships has come the movement of people, and the things they deem most important.


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[Assistant] We can understand the material culture of a people by the marine debris they create. Some of that trash will get swept into regional surface currents like gyres, but some will get caught by smaller local currents and wash up on the shore without having traveled the world. Like, there have been outbreaks of whole toys washing up on beaches, from rubber ducks to Lego dragons to Garfield phones. What do all of these things have in common?


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[Assistant] Well, like you've probably intuited, marine debris in the 21st century is mostly plastic. There are 8 million metric tons of plastic bits and debris that we don't know the origin of, or non-point source pollution, that's estimated to be in the oceans, but there's also bigger garbage out there too. Take that whole Lego dragon.


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[Assistant] It didn't travel far. It came from a wrecked shipping container that fell into the ocean after a huge once-in-a-100-years wave hit the cargo ship that was carrying it. In fact, there are thousands of shipping containers each year that fall off cargo ships due to rough weather or other mishaps.


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[Assistant] This map shows the movement of the 50,000 ships each day moving goods around the globe.


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[Assistant] Some estimates say 90% of global trade involves container ships crossing the oceans. But as ships move, they're emitting air pollution that rides on global air circulation currents through the atmosphere.


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[Assistant] And how garbage patches won't clean themselves. Our global economies depend on the circulation of goods moved by ships, and local economies depend on the circulation of nutrients that create rich fisheries, all of which leverage the dependability of ocean currents. So who's responsible for cleaning international waters, and how do we balance our societal needs with protecting the planet?


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[Assistant] Especially through weathering, which is when rocks break down by physically disintegrating or chemically decomposing. The weathering process actually removes carbon dioxide from the atmosphere by converting it into chemical compounds called carbonates that can be dissolved in water and eventually turned into rocks.


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[Assistant] And young mountains like the Himalayas, which formed just 40-ish million years ago, seem timeless, but they actually weather and erode quickly.


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[Assistant] Think that weathering of the Himalayas when they first rose, along with the Rockies and the Alps, affected the atmosphere enough to change global climates. Of course, flattening entire mountain ranges happens over millions or tens of millions of years, but we can still see weathering in action.


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[Assistant] At timescales you and I can comprehend, weathering lends that reddish-brown tinge to my bike left outside, and eats away at the facades of old buildings. But no matter where we look, weathering is the first essential step in wearing down the landscape, shaping the Earth slowly but surely. I'm Alizé Carrère, and this is Crash Course Geography.


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[Assistant] Like we learned a few episodes ago, the Earth's topography, or the shape of the land, comes from a whole bunch of different processes, some that originate inside the Earth and some on it.


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[Assistant] And the rock cycle, which is the continuous creation and destruction of rocks and minerals, is driven by both those internal, or endogenic, and external, or exogenic, forces. Many rocks form under high temperatures and pressures deep in the Earth's crust.


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[Assistant] And when they're exposed to the lower temperatures and pressures at the Earth's surface, and all the air, water, and organisms, they start to decay. Which is just part of the rock life cycle.


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[Assistant] Though each of the three rock types have distinctive characteristics based on their formation, all rocks eventually break down into finer material, which is where weathering comes in. Weathering breaks down the rocks and creates fragmented materials or sediments which become the raw material for other rocks and for the formation of soils.


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[Assistant] So one reason why weathering is so important is because it's the principal source of inorganic material in the soil, which vegetation needs to grow.


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[Assistant] If it weren't for weathering, the Earth's continental surface would just be solid bedrock. Now, once those sediments are created, they're often picked up and moved somewhere else by wind, running water, ice, and waves. And we have a different word for that process.


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[Assistant] Erosion. So we can think of weathering as prepping the rock materials to be moved, and erosion is when the rock actually gets moved.


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[Assistant] Like, we call the pieces on the top of solid bedrock that haven't moved yet the weathered mantle. And it might just stay where it is. Or, gravity could make it creep or slide or slump or flow downhill, which we call a mass movement.


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[Assistant] These are the mudslides, debris flows, and landslides we hear about that can be really dangerous and often become headline news. But before any transport can happen, from gravity or erosion, the land has to actually be broken down through one of three main types of weathering. Basically, we have to think about how rocks can break.


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[Assistant] Water that's been absorbed into the pores within the rock expands when it freezes, building up stress and causing the rock to break. This is frost action, which can break off anything from small grains to large boulders and is an important process in cold environments where freeze-thaw cycles are common. The debris that comes from frost action has a special name too.


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[Assistant] We call it scree, and we can find it at the base of cliffs and mountain ranges like the Alps and Rockies. Rocks can also get roughed up in coastal and arid environments and during dry weather periods when there's a lot of evaporation through salt crystal growth. As water evaporates, crystals can grow from the minerals that were dissolved in the water.


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[Assistant] The crystals fill up the pore spaces and other gaps in the rock and exert pressure, which forces apart mineral grains. When they fall out of rocks like sandstone, we call this granular disintegration. Like in Arizona's Canyon de Chez, we find villages built into cliff sides used by the ancestral Pueblo culture about 1,000 years ago.


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[Assistant] These cliff dwellings protected them from the elements and from enemy attack, and were a whole web of interconnected residences and ceremonial centers located in deep indentations formed in the sandstone cliffs.


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[Assistant] The weathered niches were partially formed by salt crystal growth. So whether rock is weathered with salt crystal growth or frost action, or other processes we won't get into like thermal weathering, unloading, and slaking,


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[Assistant] When rock breaks down into progressively smaller fragments without being altered by chemicals, it's called mechanical weathering. Ultimately, mechanical weathering is what turns solid rock into regolith.


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[Assistant] The reddish brown tinge on it is from oxidation, which is when certain metallic elements combine with oxygen to form oxides. The iron in my bike frame is being drawn out to form iron oxide, or rust, weakening it. And the same thing happens in rocks.


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[Assistant] When oxygen dissolved in water comes into contact with iron in a rock, the iron is removed, weakening the structural integrity of the rock. This is a form of chemical weathering which occurs when some or all of the minerals in the rock are altered or decayed by agents like water, oxygen, carbon, and other organic acids. We humans have actually contributed to a lot of chemical weathering.


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[Assistant] Like on the columns of the Parthenon, which is a temple dedicated to the goddess Athena that stood for over 2500 years on the Acropolis of Athens, Greece. Now there's a black crust on the columns from sulfur dioxide getting released in the air from burning coal and power plants, smoke emissions, burning oil, and other industrial processes.


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[Assistant] Add a little moisture and that sulfur dioxide forms sulfuric acid that corrodes certain stone surfaces. But there's plenty of chemical weathering that happens without us, too.


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[Assistant] Water is the universal solvent, meaning it can dissolve almost anything, which can then get absorbed into a rock, so it's very efficient at chemical weathering. Especially combined with carbon dioxide to form the chemical compound carbonic acid that dissolves many minerals and forms carbonates in a process called carbonation.


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[Assistant] This is the same process that gives the zing and sparkle to fizzy beverages, and even forms caves. Carbon dioxide dissolves in rainwater, and especially in humid climates, there's a lot of carbonation happening in rocks like limestone, where the main mineral making up the rock is calcite or calcium carbonate.


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[Assistant] Calcium carbonate reacts with carbonic acid to form calcium bicarbonate, which can be dissolved away in water.


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[Assistant] So just like oxidation weakened my bike frame, carbonation weakens the limestone. And when entire regions are composed of limestone, and there are a lot because there's a lot of limestone on Earth, it creates karst topography, which is where the caves come in. The word karst comes from the Karst Plateau in Slovenia, where this particular landscape was first described.


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[Assistant] Though you can also find karst scenery in southern China, Japan, Puerto Rico, Cuba, and the Yucatan Peninsula, as well as in US states like Kentucky, Indiana, New Mexico, and Florida. In a karst area, streams on the surface get diverted underground through openings in the rocks created by carbonation, which creates disappearing streams and dry valleys.


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[Assistant] There can be steep-sided gorges pitted with cavities called sinkholes, which can often collapse catastrophically. When cavities in the rock get large enough for humans to enter and explore, they officially become caves.


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[Assistant] And if they're formed by limestone rock, we call them solution caves, which usually form between two different rocks, like limestone and shale. As we enter a solution cave to go spelunking, or cave exploring, we're kind of entering a subterranean world that only exists because of chemical weathering.


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[Assistant] We might see sediment from glaciers mixed with bones of dead animals or even humans.


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[Assistant] And if we're lucky, we might see artifacts like pottery shards and spearheads from the Neolithic, Bronze, or Iron Ages. A little further in, we might walk into a roughly dome-shaped chamber, large enough to hold a tall building.


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[Assistant] They're usually made of calcium carbonate that got weathered, then carried and deposited by groundwater one drip at a time from cave ceilings and walls. The similar-looking deposits growing from the floor are stalagmites.


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[Assistant] Depending on how fast the water drips, how many minerals the water contains, and the cave atmosphere, they can look more like columns or cones. And where a stalactite joins a stalagmite, we get a column.


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[Assistant] Many stalactites, stalagmites, and columns get stained beautiful colors as iron and manganese are oxidized through oxidation. Moving through the cave, the wild scenery isn't the only difference we notice from the surface.


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[Assistant] Mammoth Cave in Kentucky in the US is the longest in the world with over 640 kilometers of mapped subterranean hollows and passages.


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[Assistant] And worldwide, it's estimated that 90% of possible caves lie undiscovered. Which might not be all bad, since cave tourism is seriously impacting these otherworldly places that took millions of years to weather.


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[Assistant] So when we emerge from our cave tour, we have to take precautions, like being careful to not reuse our gear in other caves without extensive decontamination, or even at all to avoid the spread of White Nose Syndrome, a fungal disease killing bats in North America. Finally, the action of animals and plants bring about biological weathering that helps both mechanical and chemical weathering.


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[Assistant] Like the teenage girl in Harbin from episode 3 who almost twisted her ankle on the curb while jogging.


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[Assistant] It might have been that the curve was uneven because the tree roots exerted pressure to heave the sidewalks. Other organisms bore into rocks, and bacteria, algae, fungi, and lichens can chemically alter minerals in rocks.


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[Assistant] When dead lichens leave dark stains on rocks, these spots can absorb more thermal radiation than on lighter rock, which encourages weathering. And we can't forget us humans, who have exposed bedrock by building quarries, mines, roads, and railways. And our agricultural practices have greatly changed soil and weathering processes in many regions throughout history.


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[Assistant] Weathering is a complex phenomenon, and there are no firm rules as to how different rocks will weather in different climatic conditions because minor differences in their characteristics and how much moisture is available can also control outcomes. But weathering itself doesn't work alone and depends on other processes to transport sediment and expose fresh rocks.


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[Assistant] On a hill slope, the processes of weathering, transport, and erosion are very much mutually interdependent, and form one unified system shaping the Earth. Which we'll continue discussing next time when we talk about erosion and how rivers shape our landscapes.


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[Assistant] Thanks for watching this episode of Crash Course Geography, which is filmed at the Team Sandoval Pierce Studio and was made with the help of all these nice people.


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[Assistant] If you want to help keep Crash Course free for everyone, forever, you can join our community on Patreon.


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[Assistant] I'm the real one! I must speak with the Jade Emperor!


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[Assistant] Please punish this monkey! He's pretending to be me! Punish him! Cried the other. He's pretending to be me!


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[Assistant] Maybe it will have some information about the fake Sun Wukong.


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[Assistant] Go to our website to download a free practice sheet. First, we'll write the capital O. That's the big O. Start at the top and make a big circle to the left.


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[Assistant] Now we're going to write the lowercase o. That's the small o.


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[Assistant] Next time, we'll write the letter P. Don't forget to subscribe to our YouTube channel. You can also follow us on Facebook and Twitter. See you next time!


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[Assistant] Except us. I've got some small change.


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[Assistant] It's good to see you again. I was just about to have tea.


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[Assistant] Keep this magic stone in your pocket. It will stop the wind from blowing you away.


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[Assistant] To really understand the two different violin sections' roles, it helps to know the people playing in them.


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[Assistant] Generally speaking, the most accomplished violinists will make up the first violin section.


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[Assistant] In the top professional orchestras, sometimes the difference in the level of playing between the sections is almost indistinguishable.


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[Assistant] In regional orchestras, the levels widen somewhat.


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[Assistant] While in semi-pro and amateur orchestras, the difference is liable to be fairly pronounced.


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[Assistant] This is just one more reason why an experienced orchestrator takes pains to find out exactly what kind of orchestra is going to play a specific commissioned work, and compose with foresight.


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[Assistant] The first violinists bear the greatest responsibility for stating the thematic content of an orchestral work.


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[Assistant] They're the most likely section to introduce a motive, bridge a development, or drive home a cadence.


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[Assistant] They serve not only as the face of the string section, but of the orchestra as well.


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[Assistant] The first violins also excel at leading imitation and countermelody between the strings and the other sections of the orchestra.


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[Assistant] The orchestrator should keep in mind that in contrapuntal passages with the other strings, the first will have a tendency to dominate, even if scored with care.


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[Assistant] This is due to slightly greater numbers and to more advantageous seating, not to mention a psychological tendency to lead dynamically.


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[Assistant] Of course, when the string section is playing a more harmonic role, the first violins will be playing the top note of the chord, which can lend a certain type of brilliance and projection.


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[Assistant] This can also be used to advantage in more subtle scoring for ethereal effects. Even in the most wispy of backgrounds, the first violins help define the harmonic texture in the clearest way.


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[Assistant] The specialty of the firsts is in very high playing, which they're expected to pull off without problems of intonation.


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[Assistant] Notes of extreme range are plentiful in first violin repertoire, and must sound effortless, no matter what contortions a player might go through to get it right on the money.


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[Assistant] One of the key features of the first violin is its leadership in the orchestra.


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[Assistant] As much as all the string players may be following the conductor, they're also focused on the bowing of the concertmaster.


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[Assistant] In a passage of complex rhythm or integrated lyricism, in which many players contribute, it's always the strongest when the first violins play.


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[Assistant] They are closest to both audience and conductor. They dictate the bowing, and their sound is the most unifying.


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[Assistant] But in many ways, the first violins are nothing without the seconds, which we'll see very clearly in the next video.


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[Assistant] Just before I introduced the double bass, I referred to it as the cello's partner. And in a way, that's one of its chief roles, especially in classical period scores.


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[Assistant] A quick look at the symphonies of Mozart, Haydn, Beethoven, and Schubert shows that these composers saw the double basses almost exclusively in that context.


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[Assistant] So much so, that the two instruments share a staff.


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[Assistant] Essentially, it's the cello part being doubled by the basses, with the occasional direction for the basses not to play.


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[Assistant] Let's revisit one of the main reasons for the double bass's low C string. If the lowest note of the cellos is C, and the basses are being asked to double at the octave,


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[Assistant] Then they'll naturally run into a wall with a standard E string bass.


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[Assistant] The solution is to jump up an octave as the notes approach the lower limits of pitch, doubling the cello at a unison instead of an octave.


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[Assistant] It's important to note that in passages where the cellos are occupied in other tasks besides holding down the bass line, the double basses can double at the octave with the violas quite effectively, or even other instruments like clarinets, bassoons, and horns. The trick here has to do with the harmonic series.


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[Assistant] The bass plays the fundamental tone, but it's essentially the second partial that resonates the strongest.


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[Assistant] In this way, the rest of the orchestra is strengthened harmonically by the double bass's presence.


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[Assistant] But it's important that this presence not be too strong. A very loud note from the basses can cause a filling in of the harmonic series in a string chord.


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[Assistant] With the result that the third partial can sound, or even worse, the fifth partial, which can change a chord from minor to major.


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[Assistant] This effect is particularly evident on open strings, which have a more active resonance.


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[Assistant] Fortunately, there are several factors at work that help prevent this from happening most of the time.


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[Assistant] One is the characteristic spreading of tone that occurs with several instruments on the same pitch.


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[Assistant] The other is the double bass's relative gentleness by comparison with the cellos and violins. This is another inherited trait from the viol family.


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[Assistant] The double bass is essentially a Renaissance chamber instrument.


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[Assistant] It's made somewhat stronger with modern construction techniques, but it still favors a lower spectrum of harmonics and a quieter tone.


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[Assistant] This is why the actual physical volume of 8 or 9 double basses must be used to adequately balance the tone of 10 to 12 cellos equally a quarter their size.


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[Assistant] With the development of more systematic orchestration techniques in the 19th century, the double bass became truly liberated from its position as the cello's sideman.


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[Assistant] This has to do with both the cello's growing independence as a thematic resource and increased demands of virtuosity on the bases themselves.


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[Assistant] Today's orchestral bass parts are filled with challenging passages demanding the highest degree of musicianship from players.


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[Assistant] By the same token, the bass is often called on to provide a slow, deliberate series of low notes, or even a long single pedal tone. As I mentioned before,


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[Assistant] These notes do not have to be in the bottom register to be effective.


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[Assistant] There are many imaginative treatments other than a simple long tone, like tremolo, which works great on double bass, or harmonics, or even tremolo harmonics.


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[Assistant] More than just providing the bottom note of a chord, the double bass is integral in establishing a sense of motion and rhythm in a larger texture.


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[Assistant] This becomes ever more essential as the orchestral scope increases.


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[Assistant] Hitsukado is also an important aspect of the double bass's role.


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[Assistant] While violin and viola pizzicato is somewhat dry, and cello less so, double bass pizzicato is profound.


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[Assistant] It has a way of pushing at the air in a concert hall very much like a bass drum or timpani.


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[Assistant] Here's where the lower notes really speak to their greatest effect in clarity.


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[Assistant] As useful as the double bass can be, it's very important not to overuse it.


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[Assistant] Otherwise the music becomes too much about one type of sound, large, grandiose, heavy, or even just too rich or full-blooded all the time. With over-familiarity, the ear starts to lose the significance of the double bass's presence in the orchestra. Let it breathe, and give the players time to rest their shoulders.


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[Assistant] That's how the bases work as a unit. Let's see how they fly solo in the next video.


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[Assistant] Some save as if they should live forever. Others spend as if they would die right away.


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[Assistant] Educating the mind without educating the heart is no education at all.


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[Assistant] I count him braver who overcomes his desires than him who conquers his enemies, for the hardest victory is over itself.


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[Assistant] It is more important to organize the peace.


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[Assistant] The high-minded man must care more for the truth than for what people think.


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[Assistant] Learning is not child's play. We cannot learn without pain.


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[Assistant] Without friends, no one would want to live, even if he had all the other goods.


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[Assistant] The secret to humor is surprise.


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[Assistant] You can't chase after money. You need to go towards them.


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[Assistant] For two years a person learns to speak, and then for the rest of his life, he learns to be silent.


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[Assistant] Because they are more certain they are their own.


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[Assistant] Tire Town School. Episode 32. Laying in the Dirt.


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[Assistant] Eddie drove to the construction site. He went slowly. He didn't want to crash again.


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[Assistant] You won't crash, said Dipper. Don't you wanna go fast? No, said Eddie.


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[Assistant] Zippy drove over. Hey, slowpoke, he said.


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[Assistant] As we discussed in the previous tutorial, pretty much everything you can see or feel is teeming with bacteria.


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[Assistant] The air we breathe, the food we eat, the surfaces we touch, and especially all the natural wonders around us. If you were to scoop up about a tablespoon of soil or a small cup of ocean water, scientists predict that you'd be holding as many as one million bacterial species in your hand.


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[Assistant] Many of these bacterial species might contain critical answers to some of our biggest questions in medicine, energy, and engineering, but there's a catch. We're unable to grow the vast majority of bacterial species in the lab in order to study them more closely.


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[Assistant] But more on that later. First, let's cover the basics.


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[Assistant] Of all these bacterial species, thousands cover the human body, some transiently stopping by, others taking up permanent residence. However, just a fraction, a few hundred or so, can cause disease in humans.


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[Assistant] With so many different types of bacteria out there, how in the world do we keep them straight?


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[Assistant] When we encounter an unknown species, perhaps during an outbreak, how do we identify it?


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[Assistant] How do we know what it's capable of? How can we learn how to protect ourselves against it?


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[Assistant] First, let's back up and talk about how bacteria are named.


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[Assistant] The science of classifying living beings is called taxonomy, and we've been doing it ever since Swedish botanist Carl von Linea, also called Linnaeus, established a system for classification using taxonomic categories in the 1700s.


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[Assistant] He wanted to minimize chaos as new species were discovered, and provide a structure for defining and recognizing any newly discovered species.


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[Assistant] In the case of bacteria, we use a binomial, or two-name, system of nomenclature. The scientific name for any bacteria is always the name of the genus first, which is capitalized, followed by the species name, which begins with a lowercase letter. Both should be italicized.


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[Assistant] The names of the genus and species have a wide variety of origins. Sometimes they were named after the microbiologist that discovered them.


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[Assistant] In other cases, the name might be related to how the microbe looks or the disease it causes.


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[Assistant] Now that we've covered the names, let's talk about how bacteria got sorted into their respective categories in the first place.


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[Assistant] When it comes to classifying bacteria, it may seem a daunting or even impossible task. However, scientists have developed a system to observe, test, and then categorize bacteria into logical relationships. There are three main types of classification. Phenotypic, analytic, and genotypic.


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[Assistant] Let's talk about what each of these entails, and then discuss some categories that bacteria are typically sorted into.


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[Assistant] First, let's talk about phenotypic characterization, meaning the set of observable characteristics of bacteria.


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[Assistant] Those are size, shape, and staining characteristics.


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[Assistant] Before we had the advanced technology we have now, scientists relied on observing microscopic and macroscopic morphologies of bacteria.


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[Assistant] For example, using Gram staining, a method developed by Hans Christian Gram in 1884, we can determine if bacteria are Gram positive or Gram negative, and thus how much peptidoglycan their cell wall contains.


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[Assistant] Gram-positive organisms have a thick peptidoglycan wall, retaining lots of crystal violet stain when using this method, and thus appearing a vivid blue under a microscope.


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[Assistant] Gram negative organisms have a much thinner peptidoglycan layer, which does not hold the blue dye.


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[Assistant] Even just separating bacteria into gram-positive versus gram-negative can tell us a lot about how they might behave.


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[Assistant] Certain microbes have unique staining characteristics, such as the genus Mycobacterium, which can be detected by an acid-fast stain.


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[Assistant] Another example involves identifying the shape of individual organisms under a microscope, which will be either rods, cocci, curved, or spiral.


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[Assistant] Zooming out a bit, scientists also look at how bacteria grow on agar in the lab.


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[Assistant] They look at the colonies of bacteria that grow, taking note of the size, shape, color, and even smell.


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[Assistant] For instance, streptococci colonies tend to be smaller in relation to most other types of bacteria, and serratia marcescens typically appear red when grown at 22 degrees Celsius.


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[Assistant] We can test for hemolytic properties on blood auger, identifying if the bacteria produce toxic byproducts capable of destroying red blood cells.


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[Assistant] For example, Streptococcus pyogenes, the causative agent of strep throat, is a gram-positive bacterium that forms long cocci chains and grows as small white hemolytic colonies on blood auger plates.


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[Assistant] Since it is likely for multiple species to appear similar in these types of tests, these phenotypic characterization methods serve only as a starting point for further investigation.


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[Assistant] Next, there are tests to determine what biochemical properties the bacteria have, like the ability to ferment specific carbohydrates, what carbon sources they can use for growth,


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[Assistant] And the presence or absence of different enzymes, like lipases, proteases, or nucleases.


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[Assistant] All of these observations combined can identify with reasonable precision a species of bacteria.


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[Assistant] These techniques have also been used to subdivide groups of organisms beyond the species level, down to a specific strain.


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[Assistant] Doing this by looking at the genetic makeup of the organism, especially in the case of an outbreak, is called biotyping.


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[Assistant] Many bacteria also possess antigens, which might be a toxin or other substance that triggers an immune response in the body.


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[Assistant] Grouping bacteria based on these antigens is called serotyping.


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[Assistant] Using serotyping, scientists can work backwards using antibodies to detect which antigens are present, thus allowing them to narrow down the bacterial possibilities.


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[Assistant] Serotyping is a powerful tool for classification, especially for those species that are difficult to grow, those that are difficult to test biochemically, or those that need to be identified rapidly, such as during an outbreak.


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[Assistant] Scientists can also look at which antibiotics bacteria are susceptible to, which is called analyzing their antibiogram patterns.


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[Assistant] Finally using phage typing, scientists can assess which bacteriophages bacteria might be susceptible to.


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[Assistant] Now that we've covered phenotypic classification, let's move on to analytic classification.


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[Assistant] Analytic classification methods include whole-cell lipid analysis, cell wall fatty acid analysis, whole-cell protein analysis via mass spectroscopy, and the presence of cellular enzymes via multilocus enzyme electrophoresis.


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[Assistant] Analytic classification can be a bit labor intensive, requiring expensive machines and specialized training.


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[Assistant] For these reasons, analytic classification is typically done in special laboratories.


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[Assistant] Finally, the most precise method for classifying bacteria is through genotypic classification.


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[Assistant] Put simply, this means using bacterial DNA to determine what species or family bacteria might belong to.


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[Assistant] In the early days, scientists used the ratio of guanine and cytosine to classify bacteria.


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[Assistant] As technology has progressed, so has our ability to quickly and accurately identify bacteria using DNA.


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[Assistant] Using DNA-DNA hybridization, scientists measure the degree of genetic similarity among bacterial isolates.


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[Assistant] Taking this a step further, scientists can extract DNA from an organism and expose it to species-specific molecular probes.


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[Assistant] If the nucleic acid probe binds to the DNA, then you know you've properly identified the organism.


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[Assistant] We can also use nucleic acid sequence analysis to compare unknown bacteria with already known sequences that are unique to a genus, species, or subspecies.


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[Assistant] Additionally, some bacteria carry plasmids, which are small circular DNA strands that replicate independently of the chromosome.


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[Assistant] And while the genetic makeup of bacteria can vary drastically between species, their ribosomal genes are remarkably well-conserved.


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[Assistant] Scientists routinely use 16S ribosomal RNA sequences to establish taxonomic relationships between prokaryotic strains.


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[Assistant] That's why in situations such as an outbreak or epidemiological investigation, scientists can use plasmid analysis, or ribotyping, to quickly identify bacteria.


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[Assistant] Now here's the thing, bacterial classification into families, genera, and species changes all the time, evolving as we learn more about these microscopic creatures.


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[Assistant] Generally speaking however, our classification system is a robust starting point.


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[Assistant] Using all of these techniques we discussed, we can organize bacteria into categories and predict their pathogenic capabilities.


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[Assistant] Let's look at some of these categories for medically important bacteria.


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[Assistant] First, aerobic gram-positive cocci, which can be further subdivided into catalase-positive cocci, which includes the staphylococcus group of bacteria, and catalase-negative cocci, which includes the enterococcus and streptococcus groups.


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[Assistant] Next, aerobic gram positive rods, which can be grouped into actinomycetes with cell wall mycolic acids, actinomycetes with no cell wall mycolic acids, and miscellaneous gram positive rods.


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[Assistant] Then aerobic gram-negative rods, cocci, and curved rods, which include a wide variety of pathogenic organisms.


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[Assistant] Additionally, there are anaerobic gram-positive and gram-negative bacteria, which are further grouped by shape, cocci, or rods.


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[Assistant] Now that we've gotten classification out of the way, let's talk about how these bacteria are able to cause damage to the human body.


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[Assistant] Thanks for watching, guys. Subscribe to my channel for more tutorials, support me on patreon so I can keep making content, and as always, feel free to email me at


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[Assistant] Turns out there's things you can do in school that I think are valuable, and when you're trying to pick courses and figure out where to focus your time, the classes I look back to now and think, wow, those are the ones that helped me deal with that uncertainty day to day, are the ones where day one of the quarter they tell you,


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[Assistant] We don't know what you're going to be doing for the next rest of the quarter. You'll get this at the d.school a lot and in all the entrepreneurship classes. It's your job to ask the question, figure out the question that you're going to tackle, and then answer it for the rest of the quarter. That's just a very different experience from, well, these are the ten problem sets you're going to tackle and then we'll deliver them at the end. Of course, going through those motions is really important as well.


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[Assistant] The, the, the engineering we end up doing, we, we call, uhm,


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[Assistant] So we launched on this like little machine server in Los Angeles. We had no idea what we were doing. We're like, well, like maybe some people will sign up. Within 24 hours, we had so much demand on that one machine that all of a sudden we had to scale out to like what we now have like.


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[Assistant] Millions of users. None of us had touched Amazon's cloud platform at all before launching. We'd kind of heard of it but shied away from it.


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[Assistant] And it turns out that like, there's no motivation stronger than a bunch of people knocking at your door saying, I want to use your product, like fix your thing. And you know, we put in like,


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[Assistant] A lot of, I don't really remember the first two months of our startup because we didn't sleep and I think short term memory goes out of the way.


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[Assistant] I'm told we put in a lot of late nights that we're all about saying what do we need to do to get our product to a place where people can like keep using it, get excited about it, scale to the challenge, and you'll learn those things because you're bright and intelligent, you started a company because you trust yourself, uhm,


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[Assistant] So having that faith and not shying away from a big challenge because you're like, well, what if we're successful, we won't know how to scale, like, I barely really knew how to use like a lot of the Linux, like,


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[Assistant] It's weaving a whip. That's how spiders catch their food. With a sticky silk whip.


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[Assistant] So am I. Let's go home. We have autumn berries for dinner.


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[Assistant] Of course. You run along and have fun. I'll see you later.


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[Assistant] Oh, very true. Spiders build their webs again every evening. So she's had lots more practice than you.


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[Assistant] I said, take a seat, and uhm, he sat down, and he was obviously very, very nervous. He was actually physically trembling, like this. And uhm, so I said, you know, how are you?


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[Assistant] Alright, remember to follow me on Instagram, Facebook, subscribe to me on YouTube, and you can connect with me on Weibo as well. And, um, I'll see you guys soon. Bye!


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[Assistant] Higher Town School, episode 35. Eddie is brave.


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[Assistant] Oh yeaah, said Zippy. Then cross the bridge. Fine, said Eddie. I will.


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[Assistant] I climbed up all by myself. You did too. Huh, you couldn't do that before. How did everything become different?


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[Assistant] Can you still peek through? Yes. So, nothing is different? There is one thing. What is it?


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[Assistant] I don't need to stand on tippy toes to spy through the hole. Oh, but you always used to stand on tippy toes. So the eye spy hole has moved... down? Hmm.


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[Assistant] Yes! Which do you love more, hiding or seeking?


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[Assistant] Very good. Now it's your turn. Are you ready? Here we go. Rush, catch, clap.


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[Assistant] Hull. Punch. Push. Run. Sing. Sit. Skip. Spin. Stand. Swim. Walk. Wash.


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[Assistant] Alright. This has been ELF Learning with Actions 1. Thanks for watching. We'll see you next time. Bye.


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[Assistant] All of what I'm talking about here is I'm talking from my experiences. I build software. Again, I don't build factories in India that cost a billion dollars.


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[Assistant] I don't have all of this infrastructure cost, I don't need any of all that ramp up. I'm talking about software, web 2.0, blah blah blah blah blah. In this industry, venture capital is absolutely a time bomb.


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[Assistant] And it's probably the most harmful thing you can do to a new business, is to accept venture capital upfront. And I'll tell you why. At first, it sounds like it's a really good idea.


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[Assistant] If I didn't take venture capital, well, I wouldn't have any money, and we would only be us three people, and we would actually, like, how are we gonna live? Uhm, good question. Now, if you take venture capital, you've got millions. You're probably gonna run way of years.


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[Assistant] And uhm, the worst that can happen is that you waste five years of your life. That's pretty bad.


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[Assistant] Wasting five years of your life on something that doesn't work because the time bomb blew up.


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[Assistant] Uhm, so the trade-off is sort of, are you going to have to pay now?


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[Assistant] Or you actually have to prove that your idea is good enough that it can be profitable and that it can be self-sustainable. Uhm, or you're gonna have to pain five years from now when you realize that uhm, the time bomb blew up.


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[Assistant] Now the venture capitals own your company, and they've just pushed you out.


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[Assistant] And you have nothing to show for five years of effort. That's sort of the worst case scenario. But it happens a lot more often than you'd think.


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[Assistant] I've been talking to a bunch of entrepreneurs in the Web 2.0 space, and a lot of them took venture capital.


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[Assistant] I have not met a single one who wouldn't say he would do it differently if he had to start out with today. Uhm, but there's not a lot of information out there about that because the problem is once you take your series A round of founding, you're an addict. You're gonna need that next fix.


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[Assistant] You're gonna need serious beat right now. We need some, uh, bridge capital to get it over just to the other side. Uhm, and when you're in that situation and you're an addict,


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[Assistant] It's a pretty bad idea to piss off your dealer by saying, I should never have gotten into this in the first place. I'm so sorry. Uh, no, doesn't really work. So, big warning label on venture capital.


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[Assistant] You've probably heard of cholera, at least in passing, but what is it, and what causes it?


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[Assistant] Cholera is an acute, which means severe and sudden in onset, diarrheal disease that's contracted by either drinking water or eating food contaminated with the cholera bacterium. It can be absolutely deadly if left untreated, killing within hours in some cases.


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[Assistant] The infection can range from mild to severe, with approximately one in ten cases characterized by profuse vomiting, watery diarrhea, and leg cramps.


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[Assistant] The rapid fluid loss can cause extreme dehydration and shock, which is what makes the disease so life-threatening. Let's get a closer look at this killer.