History of the Universe

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Permian Period 299 to 251 mya

Summary

During the Permian Period (named after a Russian district), the continents were assembled into almost a single land mass.

This land turned green as conifer trees replaced the lycopods and others of the Carboniferous period. They were able to invade dry land because they were able to reproduce without the presence of water. Insects also continued to diversify on land.

The Permian ended with the largest mass extinction in history.

Continents 300 mya

Earth 300 mya. Click here for key. Previous image. Next image. Image courtesy of TimeTrek

The collision of North America with Europe and Siberia, started 400 mya, was completed and Laurasia was formed, consisting of North America, Greenland, the Baltics, France and Siberia.

At the same time this northern supercontinent hit the southern one (Gondwana) and a new supercontinent, Pangaea (meaning "all land") began to come into existence. The collisions produced many mountain ranges including the Appalachians and Urals.

Northern and Southern China were still separated from Pangaea.

By this time plants, invertebrates and vertebrates had all left the sea and started to live on land.

Climate

Most glaciers melted and global temperatures rose.

Seed Plants

Dry land turned green when plants evolved from ferns able to reproduce without surface water. They did this by carrying their own copies of the wet soil with them. The egg was held near a little damp growth on the plant. The sperm was carried to it in a small grain called pollen which was blown by the wind. When pollen landed on the damp growth it could grow like a small prothallus. The sperm in the pollen fertilized the egg while it was still on the plant.

Once the egg was fertilized it developed into a seed, still on the adult plant. A seed is a baby plant wrapped up in a hard protective case. It waits for the right conditions (usually spring) before growing. Seed plants had thin needle-like leaves. They began to replace ferns around 300 mya and gradually spread over most of the land.

Image of pine after Franz Eugen Köhler

The best known seed plants alive today are the conifer trees such as pine, spruce and larch. They are important to humans because they give us softwood timber for building, furniture and paper. These trees grow fast and cover huge areas of Europe and North America. These forests are usually managed well so that cut trees are replaced rapidly. This is very different from the hardwoods of the tropical rain forest which we will meet later.

Invertebrates Free From Water

Once the seed plants had evolved ways of reproducing without surface water, there was lots of new food which animals could eat. But first they had to solve exactly the same problem that the plants had just solved: how to reproduce without surface water.

Among the arthropods the insects, spiders and many other groups evolved ways to do it. Reproduction involved the male passing his sperm to the female. Sometimes he passed her a packet containing sperm. Often he injected the sperm into her body. The female used the sperm to fertilize the eggs while they were still in her body.

Image of stag beetle courtesy of L. Shyamal

Then she covered the eggs with a hard protective coating and laid them near to some food. Insect eggs are therefore similar to the seeds of plants. When the young hatched they were able to live on land. So the insects were completely free from the need for surface water to reproduce. These animals appeared about 300 mya.

Reptiles

Soon a group of vertebrates called reptiles solved the problem of how to reproduce without water, and they did it in exactly the same way, as the insects. Fertilization occurred before the eggs were laid, by the male injecting sperm into the female’s body.

She used it to fertilize her eggs which she then covered with a tough water-proof skin and laid on land. No surface water was needed for reproduction.

Image of Hylonomus lyell courtesy of Nobu Tamura

Reptiles had scaly skin. They probably could not keep themselves warm when the weather was cold or at night-time, and may have become slow and sleepy at these times, although there is some debate about this.

Mass Extinction

The Permian ended with a mass extinction so dramatic that entirely new forms were able to evolve into the spaces left. As a result the Permian is regarded as the last period of the Paleozoic ("old life") Era. The Triassic Period which followed began a new Era, the Mesozoic ("middle life").

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History of the Universe eBook
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Written by Wyken Seagrave
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