Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure gauges or vacuum gauges. A manometer is a good example as it uses a column of liquid to both measure and indicate pressure.
Figure 1: Timeline of mass extinction events. The five named vertical bars indicate mass extinction events. Black rectangles (drawn to scale) represent global reef gaps and brick-pattern shapes show times of prolific reef growth (Veron 2008). There have been five mass extinction events throughout Earth's history: 1  The first great mass extinction event took place at the end of the Ordovician, when according to the fossil record, 60% of all genera of both terrestrial and marine life worldwide were exterminated.
Every time we pass another population milestone â at the moment, weâre tallying a whole-Earth total of 7 billion â the question arises: How many people have ever lived on the planet? The Population Reference Bureau, or PRB, has an answer for that. (Make your guess now; the answer will appear lower down.) But itâs heavily qualified, and thereâs a story behind it. The story starts sometime in the 1970s, when a notion came into common conversation that the population was growing so fast that 75 percent of the people who had ever lived on Earth were currently alive.