The first took place around 600-542 million years ago, when complex life on Earth suddenly diversified and appeared in the fossil record.
Known as the Cambrian Explosion, it is commonly thought to be the time period wherein complex life began to take over the world. Scientists have recently become aware that an even more ancient zoological band of enigmatic lifeforms, the “Ediacaran biota”, also existed prior to this date, and they disappeared from the fossil record when the Cambrian Explosion took place.
Although limited fossil evidence makes it hard to know for sure, it appears that this biological switchover wiped out the Ediacarans simply because the new kids on the block outcompeted them. Overall, scientists think that this mass extinction event was more deadly than the end-Cretaceous, but not quite as bad as the Great Dying.
The hypothetical eighth mass extinction may be the worst of all, though. When primitive photosynthetic algae converted the world’s ancient atmosphere into an oxygen-rich one 2.4 billion years ago, they thrived. However, the world was covered in microorganisms that didn’t need oxygen at the time – in fact, to them, it was a poison.
So although this is known as the Great Oxygenation Event (GOE) – something ultimately giving life to everything we can see living around us today – it is also referred to as the Oxygen Catastrophe, as it wiped out almost all other life on Earth at the same time. Although we will likely never be able to quantify how much life it killed off, it’s likely that it was the greatest mass extinction of them all.
The Times They Are A-Changing
If you had to absolutely pin down a natural disaster cause to a mass extinction effect, the volcanic activity that killed off life during the Great Dying has the claim to being the “most powerful” natural disaster. By depositing so much carbon dioxide into the atmosphere, the world’s climate changed so fast that almost all life on Earth died. However, you could also feasibly say that the GOE’s life-induced climate change was likely to be the most death-inducing of all.
The world is warming, and it's definitely our fault. Neil Lockhart