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.
A new Nature study estimates Earth is home to three trillion trees. It says 46 percent of the planetâs tress have been cleared since the dawn of agriculture 12,000 years ago. 1  A new study published in Nature estimates the planet has 3.04 trillion trees.  The research says 15.3 billion trees are chopped down every year.