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.
The last Ice Age, known as the Pleistocene Epoch, began almost 1.8 million years ago and lasted until approximately 11,700 years ago. During this time, massive glaciers covered most of the surface of the Earth. There have been four known Ice Ages on Earth in the 4.6 billion years that the planet has existed. It is very possible that there were many more that occurred that are undocumented from before the advent of mankind, about 2.3 million years ago.