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.
In the last half-billion years, life on Earth has been nearly wiped out five timesâby such things as climate change, an intense ice age, volcanoes, and that space rock that smashed into the Gulf of Mexico 65 million years ago, obliterating the dinosaurs and a bunch of other species.