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