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First living things on land clarification

First living things on land clarification (This video copyrighted under Create Commons Attribution and Share-Alike CC-BY-SA license). Created by Sal Khan.

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Video transcript

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.