The depiction of the history of the Earth, borrowed from The Times Concise Atlas of the World, shows that there have been nine mass extinctions of marine forms of life and seven of terrestrial life-forms since the Proterozoic Eon, the last of the Precambrian Age. To put these into the perspective of the various eras and periods that have existed during the Phanerozoic Eon, here is an Excel chart.
