Develop a greater appreciation for how the air, water, land, and life formed and have interacted over the last 4.5 billion years.
Video 4.6.1: How Plants and Animals Came Onshore - Dr. Victoria Egerton
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From the course by University of Manchester
Our Earth: Its Climate, History, and Processes
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From the lesson
Life, and its Effect on Earth’s Climate System
Meet the Instructors
Prof. David M. SchultzProfessor of Synoptic Meteorology
School of Earth, Atmospheric and Environmental Sciences
Dr Rochelle TaylorPostdoctoral Research Associate
School of Earth, Atmospheric & Environmental Sciences
Dr Jonathan FairmanPostdoctoral Research Associate
School of Earth, Atmospheric and Environmental Sciences
We're here at the Manchester Museum, and I'm here with Victoria Egerton,
who is a lecturer in paleobiology here at the University of Manchester.
What we want to know about is how plants became land dwellers.
Well, that's an interesting question, because prior to the early Silurian,
you pretty much mostly had green algae,
red algae and the golden algaes that were floating around the oceans.
And certainly in near shore marine habitats.
So we're seeing at the early Ordovician, the first what are known as cryptospores.
These are different spore-like structures that
we can find near shore rocks and terrestrial systems.
But we don't know whether or not they are from true land plants or not.
And we don't actually start to see the first megafossils of land plants until
about the early Silurian.
And we don't really see the combination or the suite of characters that we expect to
see in modern land plants until the mid-Silurian.
And we start to see this with Cooksonia.
What is cooksonia look like then?
>> So cooksonia is a small plant.
Probably about a few centimeters tall.
And it's just a simple branching type pattern that it had.
It didn't have any leaves, it didn't have any wood or anything like that.
Just a simple, y shaped plant essentially.
>> So what are the characteristics then that
Causonia had to develop to allow it to come onto land.
In other words, we have all these ocean dwelling plants.
They're photosynthesizing.
Now, we've got plants that, presumably, are photosynthesizing on land, as well.
>> That's true.
So, there are five main characteristics we look for.
The first one is a reduced dependence of water for reproduction.
So, with most plants, though, if you think about your mosses, your briar fights, and
so forth, they're very small, and they require water for fertilization.
And, so, with some of these earlier land plants,
they don't depend on water as much as the briar fights do.
>> Mm.
The next step is to create a cuticle.
You want to prevent desiccation from happening.
So, you want to create a waxy cuticle around the plant itself.
And also, you need to produce a cuticle or what's called an around
spores because you want to prevent the spores from desiccating.
>> Okay.
>> And the next one will be the stoma, and the stoma is really important.
This allows for respiration.
So you've created this waxy cuticle, but you still need respiration to occur.
The plants need to take in carbon dioxide, but also release oxygen as a byproduct.
And so these little stomas, or respiration releasing structures, basically forms.
And then, we also have the formation of a root system.
So, the plants need to stay put and they need a way to get nutrients and
water to it.
And so that's where you start off with the basic root system,
which are these basic hair-like structures and then they get larger and
larger until you start to see true roots like you see with trees today.
And then the last one is that you need to create a vascular system.
So, in the water, plants can use
water to just kind of float or to get vertical if they need to or if they don't.
And also to keep them together.
But on land, they have to defy gravity now.
So they need to be pulling up the water and
the nutrients to the most distilled part of the tissues.
So this formation of a vascular system was really, really crucial for
these early plants.
>> So we have create some kind of a negative pressure gradient within these
capillaries then to pull the water from the soil from low down up to
in the case of cooksonia just a centimeter or two away from the ground.
>> Absolutely and a big part of that is through transpiration.
And that's really what drives that negative pressure.
>> Okay.
And so the transition then from these small,
little podlike plants to what we think of now,
trees, grasses.
How did that happen?
>> Well it was a definitely a very gradual process.
So you start to see, so as I said.
The Cooksonia occurred during, around the Mid Silurian.
And it's not really until the Devonian that you start to see leaves forming.
And then later on in the Late Devonian you start to see
the secondary xylem starting to form, which is wood.
And once wood was produced and
you have these leaves that can increase the surface area for photosynthesis.
Then you can start to get the really giant trees that you start to see
in the Carboniferous.
>> We just talked about the five different adaptions that plants had to make
in order to come onto land.
Is this similar, different to what the transition that animals had to make
to come on land as well?
Well, essentially, some of the main features that plants had to adapt,
animals had to adapt, also.
So, for example, they had to create some sort
of outer covering to prevent them from desiccation, just like plants did.
So, plants developed a cuticle, arthropods, a hard exoskeletons,
and then, with amphibians to reptiles, a very thicker epithelial tissue.
And that prevents the cicaction.
But also you have things like respiration structures that had to be developed.
Because it's much easier to get water from the.
Get oxygen from the water.
As opposed to through the air.
And so a specialized structure had to be developed.
Once you make that transition to the air.
But also reproduction.
So, today amphibians and fish, they require water to reproduce,
to lay their eggs.
And also to fertilize the eggs too.
But, once you get a thicker seed coating, you can then
lose that dependence on the water, and so just like with plants, plants develop this
seeded coating to protect the different reproductive structures.
But that also goes for animals too, like the reptiles.
They are thick, leathery eggs.
>> Great. Right.
So we just talked about plants' evolution onto land.
How does animal evolution compare in terms of time?
Which came first and were adaptations and improvements in one type of evolution,
say the plant evolution, driving the animal evolution forward as well?
>> Well, essentially you had to, and you needed to get some sort of
plants onto land first, before you really get any sort of animals coming on.
Because there's no reason for animals to just come onto land, for one thing.
But if you have some sort of new food source,
that can drive most any organism into a new environment.
Even if that environment may seem quite harsh.
Now, something interesting to note, is that, before there were plants on land,
there were microbes and microbial as well as fungus.
>> Mm. >> And that's what
led to the soil development to allow for plants to come onto land.
And if it wasn't for that development plants wouldn't have come onto land.
So they kind of build on top of each other.
And so after the plants came onto land, that was followed by arthropods.
And then that was later followed by invertebrates.
So, it's just one step to the next.
>> Great.
Thank you so much.
>> Thank you.
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