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.
How Many People Have Ever Lived on Earth? is one of PRB's most popular articles. First published in 1995 and updated in 2002, this latest 2011 article includes data through mid-2011 and a short video explaining the estimate. (October 2011) The question of how many people have ever lived on Earth is a perennial one among information calls to PRB.