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Fossils hold the secrets of primeval climate change

Posted in Animals, Geography, Geology, Nature, Plants, Science on Wednesday, 30 January 2013

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This edited article about fossils originally appeared in Look and Learn issue number 111 published on 29 February 1964.

Livingstone and fossil, picture, image, illustration

The young David Livingstone was a keen fossil hunter by Peter Jackson

Two hundred million years ago the world’s climate was much warmer and more moist than it is today, and the land that is now Britain was a wilderness of sand and swamp. Along the swamps grew thick, creeping undergrowth and giant ferns as big as oak trees.

Man had not yet appeared on the earth and most of the animals were gigantic creatures called dinosaurs. Some of these huge reptiles were a hundred feet long, twenty feet high, and weighed over a hundred tons.

One day in that distant period of the world’s history two dinosaurs strolled side by side along the edge of a swamp, leaving behind them a trail of huge footprints.

We know about that stroll because their footprints were made in what became the bottom of a Dorset quarry and can now be seen in a collection of fossils at the Natural History Museum in South Kensington, London.

Fossils are the traces of animals and plants that lived or grew on the earth millions of years ago and have remained to tell us what our world was like long before man was there to see it.

If you look at the face of a cliff or the sides of a quarry you will see that the rock walls are made up of layers one above the other. Geologists, the scientists who study the formation of the earth, call these layers strata.

At some period during the past ages of the earth, each strata was once on the surface of the ground, and on that surface animals and plants, quite different from any we know today lived and grew.

Throughout the history of the world its surface has been constantly changing. What were once seas became dry land, and what were once continents sank and became ocean beds. This occurred several times in the course of thousands of millions of years, and each change meant a new strata of rock.

In other words, the outer crust of our earth is rather like a pile of sandwiches all made from different kinds of fillings. And embedded in each layer of the pile of sandwiches are the remains of the animal and plant life that existed when that particular layer was at the top of the pile.

Many of the layers were quite soft when they were on top of the pile and then throughout the ages hardened into rock. In this way, footprints of prehistoric animals were made in mud and sand which were later covered with mud which gradually settled into a layer of solid rock.

But it is not only footprints that have been preserved in this way for hundreds of millions of years. There are fossils of whole animals and other creatures and of complete plants.

When an animal, whether some kind of tiny shell or a giant dinosaur, died, the flesh parts of its body either decomposed (rotted away) or were eaten by other animals. The hard parts of the body, however, such as the bones or teeth or shell, were not so easy to destroy.

Sometimes the actual skeleton is preserved. This happens when animals have been trapped in bogs and quickly buried. More often, however, the skeletons are petrified; that is turned to stone. This is done by water from the surface of the ground carrying mineral matter into the pores of the bones.

Other fossils are what are called moulds. Chemicals in water seeping through the ground eat away the buried bones so that a hollow is left in the rock corresponding to the shape of the animal, buried there when the ground was soft.

Later, mineral matter may be carried by water into the mould. This eventually results in a rock cast of the object.

By studying animal and plant fossils it is possible to build up a picture-history of the world going back for over a thousand million years. Certain kinds of fossil are found only in certain kinds of soil layers. As geologists know how long it took for the rocks to form, they can tell how long ago these forms of fossil existed.

Fossils also tell us a lot about how the world’s climate has changed in millions of years.

In the Antarctic regions, for example, fossils have been found of animals and plants which could exist only in hot climates. This proves that where there is now ice and snow there was once a tropical world.

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