Now it also lists photosynthesis starting
here, but that was actually early photosynthesis.
Early photosynthesis was anoxygenic photosynthesis.
Oxygenic meaning oxygen-creating.
An- means not.
Early photosynthesis was a less efficient form that did not create oxygen.
So early on there was chemosynthesis from materials in the water and the
atmosphere, and the beginnings of photosynthesis, but very little oxygen.
Somewhere, and it's a little controversial on
precisely when it happens, but certainly by
here the end of the Archaean, Archaean not surprisingly similar to the name archaea.
Certainly, by here, the
first oxygen-creating photosynthetic microbes appear.
This is a pretty amazing thing.
Now remember what I told you before, for these things like these methanogens.
Oxygen is toxic, and suddenly a microbe develops,
it starts to pump oxygen into the atmosphere.
What happens when it pumps oxygen into the atmosphere?
Well there are plenty of things around to react with the oxygen.
Oxygen can react with iron.
Iron was on the surface of the Earth.
Oxygen quickly reacts with iron and forms these huge bands of rust that you
can actually go and find where the sea floor sediments were banded in rust.
They're called these banded iron formations.
They're, they're incredibly cool.
They look sort of like this.
Here's a picture of a, of a sort of small one.
And you can see what happens.
There are these successive oxygenation events.
Oxygen is available in, in these periods, and all
the sediments are rusted and fall to the bottom.
Suddenly, oxygen is, is not there.
In these anoxic environments you get the iron, oxygen available again, red rust,
and you get these banded formations where you have iron, rust, iron, rust.
And they're found throughout the world.
It's a global event that's taking place.
These particular ones are from about 3 billion years ago.
Eventually though, there was nothing left for the oxygen to,
to chemically react with on the surface of the Earth.
And so, it started going into the atmosphere, and
the atmosphere started to rise in O2 based on these
photosynthetic bacteria that were very efficient at creating energy for
themselves and expelling this terrible, terrible poison into the atmosphere.
In, in a really short amount of time, the atmosphere went from this CO2, CH4, H2,
H2S atmosphere to suddenly oxygen being an important constituent in that atmosphere.
This, in general, is called the Great Oxygenation Event.
We like to call it great because we breathe oxygen.
But there's another way to think of it,
is that oxygen is a terrible, terrible poison.
So from the point of view of all of these things that presumably died out because
the atmosphere had been poisoned, this is also called the Oxy, Oxygen Catastrophe.
Once the Oxygen Catastrophe, Great Oxygenation happens, and, and
look, this was about half of the history of our
planet, half the history of our planet, we would've
been CO2, CH4, H2, H2S dominated, suddenly oxygen comes in.
Oxygen has a couple of other great effects.
Oxygen eventually leads to the creation of ozone, and an ozone layer.
And as we know, ozone protects us from
some of the ultraviolet radiation of the sun.
Ultraviolet radiation of the sun is one of the things that can cause mutations.
So, perhaps the, the, Great Oxygenation Event is one of the things that led to a
little bit more stability, that led to things
like multicellular life here in the light blue.
Sometimes, when you're talking about the history
of the Earth, you'll hear the phrase Precambrian.
I'm sure everybody's heard that.
We're talking about Hadean ,Archean Proterozoic, but Precambrian
really prefers to basically everything before about this time.
