Name_________________________
Evolution of Plants on Earth, Simplified Version in Free Verse
In the beginning, after Earth had formed, there were oceans and land
But the air had no oxygen, so there was no Ozone Layer, nothing to block UV rays
At least on land, can’t grow there. Yes, but ocean waters block UV rays, so
That’s a great place to start life. And so it was, in the water. Bacterium, then archea to eat sulfur, and
At long last, maybe 3 billion years ago, some of these Protista or Algae did the first photosynthesis.
Miracle, miracle, even though it was a single and simple cell. In the oceans. Lots of ‘em. The first plant.
Life was simple, for these plants, get your CO2 and H2O from the waters surrounding you. Pump out a
Ton of Oxygen gas, stuff we know as O2. Well, a funny thing happened at the O2 convention, some of
Them got together and formed O3. Which we call Ozone. And off they went to the Stratosphere,
Where they happily absorbed lots of ultraviolet radiation. This got them warmed. This suddenly made
Life on land possible. For animals. Not that many lived then. And plants. They did live, but not on land.
Now, most were single celled. Not much advantage in a plant getting real big, at least in the ocean.
Well, a funny thing happened to some of the algae that washed up to the shoreline. They managed
To stick to the rocks, and to get CO2 and H2O from the air. The first land plant. A kind of moss. 450MYA.
Life was good. They used spores to reproduce, like the algae used to do. But the spores were lighter, so
They could float on air. The roots that held on to the rocks, that’s all they did, hold on to the rocks.
Life on land was more difficult in ways than in the ocean. In the ocean, each plant cell was surrounded
By water – no need to worry about getting some. And floating around usually got you good sunlight.
Things were different on land. Yes, CO2 was available in the air, but getting H2O was the big problem.
And no floating around like in the oceans – if a moss plant already had “dibs” on an area, you were out
Of luck. Until plant plumbing. About 400 Million Years Ago. Your textbook calls it a Vascular System. It
Means tubing to carry water where it’s needed, where photosynthesis is happening. And to take sugar
Energy to other parts of the plant. A couple of radical effects from this vascular system. First, the plants
Could now grow taller than the moss, and steal some of that precious sunlight. Second, now it could use
Roots to collect water from the soil, so it could live in dry areas better. Ferns were the major plants to
First use this system.
And so the ferns took over the lands. Call it about
360MYA. There were so many ferns, it’s called the Carboniferous Period, since their remains got
Turned into coal beds. Not to mention, oxygen levels rose to 35%. Wow! Compared to 21% today.
Plants were royalty then, and the Fern was the prince of plants. But they could go only so high, and they
Still used spores to reproduce. Which leads to the next evolutionary development, about 319MYA. One
Thing about spores, they didn’t protect the baby plant, and they needed a moist area to sprout. So, a
Tough coat around a seed will let it survive better, especially if its coating takes several days of moisture
Before it breaks down and lets the baby seed grow into a young plant. These new guys are called the
Gymnospores. That’s Latin for “naked seed”. It’s not entirely accurate as a name, thanks to the coating
To protect it, but there is no fruit or nut attached to it. You may know them as “pine trees”, but it
Includes a ton more than pine trees, things like cedars and firs and gingkoes. And they could go places
Where the ferns and mosses couldn’t survive. Plus, they developed lignin, a tough compound that lets
Water travel longer distances through a plant’s vascular system. And to grow taller, taking sunshine
Away from those pesky ferns. Take that, you ferns! Gymnosperms rock, and for awhile, they were king.
That’s when Angiosperms came along. That means flowers, about 165MYA. Big deal, you say. Well, it
Has some big deal effects, because for the first time it gets some other organisms – animals – help the
Plant with its reproduction strategy. Kind of like hidden teamwork. A bee that gets pollen from a
a flower, doesn’t think it’s a teammate of the apple tree, but it is. Because on the way in to get
The pollen, the bee brushed by the part of the apple flower that has the “egg”. And so the bee passed
On pollen it got from another tree. Wow! Cross pollination. Lets evolution happen in a major way, and
Explains why there are so many more Angiosperms than Gymnosperms and mosses. One of the last
Angiosperm to evolve, were the grasses. About 40 MYA. Surprise, eh? Not when you realize that the
Climate was going through some big changes. For a time, carbon dioxide levels went way down, and the
Grasses are good doing photosynthesis even with super low carbon dioxide. There were also times
Big droughts occur. When that happens, trees die, but grasses go into a sort of hibernation, they can
Wait out the drought, and they are good at getting CO2 in without losing a lot of water, so they totally
Thrived when carbon dioxide levels went down. So, the grasses were the last major plant group.
To evolve.
The end?
No way.
Ocean temperatures are rising.
The ocean is getting more acidic.
Extinctions are happening, big time, in the plant world.
Funny thing, most people can’t name a single plant that is now extinct.
But when it comes to animals, they can. The Dodo Bird, the T-Rex, they are the poster children.
Of extinction. Of animals.
There is no poster child of plant extinction.
And no poster child of a new species of plant.
But, whether it is evolution at its own pace, or genetic engineering, evolution of plants will
Continue.
To be continued.
Study Guide for Plant Test
1. What process makes a plant a plant? The name of the process __________________________
That process in words: ___________________________________________________________
______________________________________________________________________________
That process stated chemically: ___________________________________________________
2. (a) Provide a timeline for plant evolution, showing the change, the millions of years ago, and the
adaptation. You can use a diagram or sentences.
(b) Explain the benefit of each adaptation.
3. What is a gymnosperm?
4. What is an angiosperm?