Did evolution itself cause a mass extinction event?
We often imagine mass extinctions to involve an apocalyptic event, whether that’s a huge meteor impact or the eruption of a super-volcano. This couldn’t be more different from the world’s first mass extinction event that we know about, which took place some 540 million years ago. This was way before any dinosaurs roamed the Earth; it was actually an immobile, tube-like creature called an Ediacaran that was wiped out.
They were essentially killed off by their own evolution, and the development of other complex life. Some of them evolved into modern animals such as molluscs and jellyfish, while other organisms that had found a way of harnessing the Sun’s light and using it to create energy, a process we know as photosynthesis, also contributed to their demise. This in turn released oxygen into the atmosphere, which was actually a poisonous gas to many of the microbes that had thrived in an oxygen-free world for billions of years. The gas that humans need to survive ironically was once the world’s first pollutant.
Evolution is of course a very slow form of mass extinction, but its importance in such events should not be underestimated. It can be just as damaging to certain organisms as a volcanic eruption or the spread of a lethal virus.
THE FIVE GREAT EXTINCTION EVENTS
End-Ordovician mass extinction
This was the first of the traditional five big extinctions, and was probably the most severe. Almost all life resided in the sea at this time, and around 85% of all these species were destroyed.
Late Devonian mass extinction
Roughly 359 million years ago, significant environmental changes caused a lengthy extinction event that killed many major fish groups and stopped the formation of new coral reefs for 100 million years.
End-Permian mass extinction (the Great Dying)
This is the most significant of all the extinction events, wiping out as much as 97% of species that left fossils behind. It had the greatest affect on the Earth’s ecology.
End-Triassic mass extinction
This extinction event made dinosaurs the dominant land animal, killing off many of the large amphibians and other mammals that were present around 201 million years ago.
End-Cretaceous mass extinction
This massive asteroid impact 66 million years ago is often blamed for ending the dinosaur’s reign on our planet.
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