We all know the dinosaurs went
extinct. Okay, most of them. But that was not the first ‘Great Extinction Event
that Earth has suffered. Since I’m really only aware of that one and its
possible cause, I decided to investigate the first one, just to see what I
could find. Apparently, it was caused by oxygen!
I know, right? Something we think is
a good thing, yet it caused a massive die-off! How could this be? Let’s take a
look.
First, let’s be sure we understand
what an extinction event is; it is a widespread and rapid decrease in the
biodiversity on Earth. Estimates of how many extinction events we’ve already
had range from 5 to as many as 20.
Most life on Earth is microbial and
thus difficult to measure. Therefore recorded extinction events are those that
affected the easily observed, biologically-complex component of life on Earth.
Normally, extinction of various lifeforms occur at an uneven rate. An
Extinction Event is when a lot of different lifeforms go extinct at pretty much
the same time.
The Oxygenation Crisis occurred
around 2.45 billion years ago, but technically, as I studied it further, it is
not considered one of The Great Extinction Events. Maybe because it’s hard to
find fossils from that long ago, so they can’t be sure what died off and in
what numbers, but it was big enough that the fossils they have found indicate
something happened.
From what I understand, Earth’s
atmosphere at the time had next to no free oxygen in it. But then
photosynthesizing cyanobacteria (which some call blue-green algae) evolved in
the shallow sea that covered most of Earth. The cyanobacteria did what it does,
and in the process, released free oxygen into the water. Eventually, the water
couldn’t hold any more of it and released free oxygen into the air. All this
free oxygen (which was a mere pittance compared to what we currently have in
our atmosphere) played havoc with the metabolism of most of the living
organisms at the time and a great deal of them died.
And the cyanobacteria continued putting
out more oxygen.
Which opened the gates for more
complex biolife forms.
So, extinction events are not always
a bad thing... if you aren’t a species that is going extinct. But they do tend
to create ‘bottle-necks’ of survival, which are followed by much evolving and
diversification to fill all the empty niches that result.
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