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First living things on land clarification | Cosmology & Astronomy | Khan Academy


In the video on the Cambrian
explosion, I talk about how surprisingly, or
somewhat surprisingly, that animals were the first to
colonize or to move on land. They did that before plants did. And someone brought
up what I thought was a very good question. If the animals were the
first, what did they eat? So I thought that was
one, a good question. So it justified a whole
video on clarifying exactly who was
first on the land. So right here, this is a
picture of algae on the coast. This is kind of algal
scum right over here. So this right here is algae. And just to be clear,
sometimes cyanobacteria, which we talked about as the
first photosynthetic organism, sometimes that’s called
blue-green algae. But that’s really bacteria. Algae is considered
to be eukaryotic. And it just doesn’t have the
structures of modern plants. So this is algae right here. And our best estimate
is that algae actually colonized kind of coastal rocks
about 1.2 billion years ago. So this is 1.2 billion
years ago, “g” giga, billion years ago. So if you wanted the first
thing that even resembled or was close to plants or animals,
and if you consider algae close to a plant, then this
would be the winner of who got on land first. This is 1.2 billion years ago. Now in the last video where I
talk about animals colonizing the land first,
they weren’t animals that only existed on land. They would have been
animals that probably spent most of their time in the ocean
collecting food or whatever. And then they would show up
on the land maybe to lay eggs. And if you think about
it, back then the land would have been a
really good place to lay eggs because
there wouldn’t have been much else on the land. So you would have been
protected from predators. So it might have been
slug-like creatures like this. Some people talk about kind
of spider-like creatures. But it still would
have been at the coast. And these would
have been creatures that would have spend a
lot of time in the ocean and some time in their land. So this is what I was
referring to as kind of animals colonizing the
land before plants. And this would have happened
about 530 million years ago. Now, the first living organisms
to fully live on the land, their whole life is on the
land, those would be plants. So it depends if you think about
things that part of their life, you’d get the animals. Things that lived their
whole life on the land, then you go back to the plants. So this right here,
this is what we think the first primitive
plants would have looked like. And the evidence–
we actually don’t have fossils from these
plants themselves. We have fossils of their spores. But we think that the earliest
fossils of their spores, which show that
these existed, were about 475 million years ago. So this is– let me do
this in another color– this right over here is
475 million years ago. So 1.2 billion years
ago, you have the algae. 530 million years
ago, we have evidence of things kind of
oozing out of the ocean and maybe laying their
eggs or something. 475 million years
ago, we have evidence of what we would kind
of call really plants. But the evidence is really
the fossils of their spores. And then the first
evidence of real– I guess you could
call them animals that spend their entire life on
the land, the oldest fossil we have– it was discovered
in Scotland fairly recently, in 2004. And this is the fossil
right over here. It was actually discovered by
a bus driver, by Mike Newman. Mike Newman, who is a
bus driver in Scotland. And they actually named
the thing after him. It’s called
Pneumodesmus newmani. So they got the newmani
from Mike Newman. And this fossil is
428 million years old. And right now, it’s
the oldest fossil we have of a true land animal. So if you think about true
plants versus true land animals, things that spent
their entire life on the land, the plants do win out. If you think about things
that spent part of their time on the land, then the
animals probably won out. If you view algae as plants,
then the plants won out. So it depends where you
want to draw the line. And this first fossil,
this is of a myriapod which just means a lot of legs. Let me write over
here, myriapod. You probably know
the word “myriad.” Myriad means a bunch of
things or a huge amount. So myriapod, a huge
amount of legs. And you might be familiar with
the millipedes and centipedes. Those are myriapods. And so those first primitive
myriapods, 428 million years ago. And they would have lived
off of plants, and maybe other myriapods,
and other slugs, and whatever other animals
they might have found. They mind have looked
something like that. So hopefully, that gives a
little bit of clarification over– it wasn’t like you
had dogs sitting on the land and they had nothing to eat. It’s kind of a gray area in what
you define a plant or an animal and who gets kind of
the bragging rights for being the first on the land. And it depends on really what
you consider a plant or animal and whether spending
part of your life on the land, whether spending
part of your life on the land will actually qualify.

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