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.

Even though the pace of evolutionary change has been accelerating during the past half billion years, it seems rather surprising that historical mass extinctions should be fairly evenly spaced. But, perhaps this is explained by extraterrestrial happenings.

Today, we are in the middle of the eighth mass extinction of self-reproducing forms of life on land, as some have been studying during the past few decades, especially since John Leslie wrote The End of the World: The Science and Ethics of Human Extinction in the 1990s.

Of the several existential risks facing humanity today, abrupt, irreversible climate change is the most immediate threat, requiring us to make major changes to the way we live our lives if we are to face the death of our species with serenity and equanimity.