Biodiversity Flourishes in Phanerozoic Eon

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Biodiversity Flourishes in Phanerozoic Eon : Cambrian explosion and biodiversity in the Phanerozoic Eon

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The earth is now starting to get closer
to being hospitable to people or animals like us
In the last video we saw, during the
Proterozoic eon, oxygen began to accumulate
in the atmosphere.
This actually caused this first snowball earth
and this mass extinction of all the anaerobic species
that made conditions suitable for eukaryotic cells
and maybe even more important,
these eukaryotic cells were able to form
multicellular organisms, and we see where that starts
right here on this chart.
Multicellular life starts right over here.
And I want to be clear, all of these things are moving targets
as we discover more things in the geological
record and we get more tools at our disposal
these numbers get tweaked.
But they do give you a good sense,
based on our current understanding
of when these things start to appear.
And coinciding with multicellular
life, and this is interesting in its own right
because it has its own meta-level effect on evolution,
you actually start also having sexual reproduction.
And what's interesting about this,
why this has such a big impact on evolution,
we talk about it a lot in the biology playlist,
is before evolution, variation in DNA had to be
completely dependent on mutations and random movements
within DNA and maybe some viruses.
Now with sexual reproduction, you had
a systematic mixing of DNA,
so that you got more variation in the gene pool
which allowed more selection, more variance to select for
and so you kind of had an acceleration
in the actual pace of evolution.
We're talking, I've looked at a bunch of sources,
they say from 1.2 billion, 1.5 billion,
a little bit over a billion
you start having these multicellular lifeforms
and sexual reproduction.
The other thing that we talked about from
the Proterozoic eon, is the accumulation of oxygen
allowed the ozone layer to build up.
Ozone is just three oxygen atoms, it is O3.
And by the end of the Proterozoic eon
so we're talking about 550 million years ago
(give or take a hundred million years)
(these are all moving targets)
the ozone layer was dense enough to protect
the land from UV rays, we talked about that
in the last video.
The Earth is being bombarded with UV rays
and the ozone layer is the only thing that
keeps us from being seriously irradiated by the sun
and allows land animals to actually live.
And so coinciding with that time
period, around 550 million years ago,
you start to have life colonizing,
especially significant life colonizing land.
Life colonizes the land.
And this was an interesting, when I first learned it,
kind of an "Aha!" moment.
You always assume that trees and grasses
are part of the background,
they come part and parcel with land,
but it turns out that animals colonized land
before plants did.
Plants didn't come into the picture before about
450 million years ago, give or take a few tens of
millions of years.
And so we're now entering the end of the
Proterozoic eon.
Life has started to colonize land,
we now have an ozone layer,
and actually there's another snowball glaciation
or snowball earth near the end of the
Proterozoic eon, and there are a bunch of theories
about why it came about and why it disappeared
maybe there were volcanoes
greenhouse gases, who knows.
But as we enter the end of that,
we start seeing life begin to flourish.
And it starts to really flourish as we enter
the (I always have trouble saying this)
Phanerozoic eon
It's not even labelled here.
The Phanerozoic eon is this chunk of time
right over here, let me write it out.
This right over here is the
Phanerozoic eon.
These divisions right here are eons
and then they break into eras.
Eras are subsets of eons.
They're hundreds of millions of years.
This is the Paleozoic era,
the Mesozoic era and the Cenozoic era.
And that's actually our current era.
But perhaps the most interesting,
I don't want to pick favorites here,
but it's one of the most interesting times in the
geologic era
is the first period in the Paleozoic era,
which is the first era in the Phanerozoic eon -
and that's the Cambrian period.
You might have heard of it before,
that's about this period of time here.
Cambrian. And during this period of
time, the earth experiences what we call
the Cambrian Explosion. That's because there
was just this explosion in the number of species
and genera that existed, the biodiversity
on the planet.
It might just be that we had the ozone layer protecting us,
things were colonizing land,
it was an oxygen rich environment.
We start seeing complex multicellular organisms,
it's about that time.
If you fast forward maybe a few tens of millions of years,
you start seeing the first fish,
the first pre-amphibians or proto-amphibians.
You fast forward a little bit as we get out of
the Cambrian period, we start seeing
plants, so they draw it right over here.
And of course these are moving targets depending
on what we discover in the fossil record.
And for me, the big "Aha!" moment here is
so many of these things you consider fundamental to
what Earth is a relatively recent phenomenon.
Plants weren't on land until about 450 million years ago.
Insects weren't on land, or did not even exist
until about 400 million years ago.
Reptiles didn't exist until 300 million years ago.
So we're about right over here now.
Mammals didn't exist until 200 million years ago.
Birds didn't exist until about 150 million years ago.
The whole dinosaur age, which we consider
in our distant past, that's essentially the Mesozoic era.
So this is essentially the age of the dinosaurs.
When you look at your time clock you see
it's a relatively recent time period,
and it actually ends with, we currently believe,
a huge rock, a 6-mile diameter rock
colliding with what is now
the Yucatan Peninsula in Mexico, right off the coast
of the Yucatan Peninsula.
And it destroyed all of the large land lifeforms ,
especially the dinosaurs.
And to put all of this in perspective,
and actually the thing that really was an
"Aha!" moment for me,
plants are 450 million years ago,
grass I view as this fundamental thing in nature,
but grass has only been
around for about
(I've seen multiple estimates) 40-70 million years.
Grass is a relatively new thing on the planet.
Flowers have only been around for 130 million years.
So there was a time when you had dinosaurs,
but you did not have flowers
and you did not have grass.
And so you fast forward all the way,
when you look at this scale it's funny to look at,
this is where the dinosaurs showed up,
this brown line is where the mammals showed up,
so the dinosaurs showed up along with the mammals
and then of course the dinosaurs died out here.
Our ancestors, when the giant rock hit the earth,
must have been burrowed in holes
and were able to stash some food away,
or who knows what, and didn't get fully affected.
I'm sure most of the large mammals were destroyed,
But what's humbling or almost humorous or
almost ridiculous when you look at this chart,
they put a little dot, you can't see it here,
2 million years ago, the first humans.
And even this is being pretty generous when they say
first humans, these are really the first pre-humans.
The first humans that are the same as us,
if you took one of those babies
and you brought them up in the suburbs and
gave them haircuts and stuff, they would be
the same thing as we are,
those didn't exist until 200,000 years ago.
200,000 to 400,000 years ago, I've seen estimates.
So this actually a very generous
period of time to say first humans,
it's actually 200,000 years ago.
And just to give you an idea of how new we are
and how new our evolution is, it was only
5 million years ago, and I mentioned this
in a previous video,
it was only 5 million years ago.
So this is just to get a sense.
This is 0 years.
Homo sapiens sapiens only around for 200,000 years.
The neanderthals, they were cousin species,
they weren't our ancestors, many people
think they were - they were cousin species,
we come from the same root,
although there are now theories that they might have
remixed in with homo sapiens, so maybe some of us
have some Neanderthal DNA,
and it shouldn't be viewed as an insult,
they had big brains, well,
they didn't actually have big brains,
they had big heads, but that seems to imply big brains
but who knows, we always tend to portray them as
somehow inferior, but I don't want to get into the
political correctness of how to portray
neanderthals, but anyway but this is a very small
period of time.
If you go 2 million years then you get to
the pre-human ancestors and
our family tree, only diverged from the chimpanzees
5 million years ago. If you draw that on this clock
it would barely make... it would be like 2 pixels
or maybe not even 2 pixels,
is when we diverged from the chimpanzees.
So hopefully that gives you a sense of things,
at least for me it really puts things in perspective.