The Evidence

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The Evidence

People are always interested in old things, antiques, old books and history. Fossils are another favourite.

  • What are fossils?
  • Where do they come from?
  • What do they tell us?

There is also a lot to be known about the rocks and soils that give rise to these fascinating things. But we often just overlook them as just being rock and soil.

However they can all give hints and evidence towards understanding one of the big questions:

The origins of life.

Fossils are the remains of organisms that lived millions of years ago. Usually all the original tissue has gone and only the shape is left as a mineral cast.

What are the fossils made from?

Most of the fossils that you find are made from the hard parts of animals. They include such things as teeth, bones and shells.

Fossils are thought to have been buried in silt or mud and broken down only very slowly. Gradually they were replaced by minerals from the surrounding ground as the surrounding ground was turned to rock. So the rock-like substance of the fossil was formed but stays separate and distinct within the rock. It lies there until you dig it up!

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Other fossils can be different in that they come from the softer parts of animals or plants. An example of this might be the 'petrified forests' that have been found in coal mines.

Petrified means 'turned to stone'. The trees that used to be in a forest where the coal mine's are were slowly turned into mineral fossils. They look like tree stumps and trunks made of coal.

But it is very rare as the conditions were not often right or the rate of decay slow enough.

What conditions are necessary?

Usually a dead plant or animal is broken down very quickly by decay and its molecules used by other organisms.

However if the environmental conditions are suitable the decay process can be slowed so that it takes thousands of years for all the tissue to disappear.

If the dead organism is covered by mud or silt no oxygen will be present. Without oxygen the bacteria and other organisms involved in decay cannot break it down.

Another example is if the tissue were covered in sap or resin from a tree keeping the oxygen out. Over thousands of years the resin turns into the yellow, stone-like mineral called amber.

Have you seen the film 'Jurassic Park'?

Remember the mosquito in the amber?

Maybe you need to do some film revision too!

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Glaciers are another favourite place for animal and plant remains to turn up. There it is too cold for microbes and bacteria that cause decay to work.

The bodies of woolly mammoths have often been found in the frozen, tundra of Siberia, some are 23, 000 years old.

In 1991 in the Oztal Alps between Austria and Italy a man's body was discovered wonderfully preserved. It was named 'Otzi' and was found to be 5300 years old.

Many other human remains have been found in the waterlogged peat bogs of northern and western Europe. The bogs are too acidic for the normal decay.

They've been found in Britain too! 'Lindow man' was found in Lindow Moss in the early 1980's.

Fossils and the tissue remains give an idea of the organism's shape and structure.

We can work out the remains and fossil's age by looking at the rocks and soil in which they are found.

To do this scientists need to know the age of the rocks and soil themselves. As organisms died and fell into the mud, resin or silt they were slowly buried by more material falling on top.

So if you know the age of the rock surrounding the fossil, you know the age of the fossil itself.

So as time went on younger and younger material covered the fossils. Therefore the deeper you dig down the older the rocks that you are cutting through.

In the Grand Canyon in the USA, the one mile deep hole stretches down to the oldest rocks at the bottom which are about 1 billion (1,000,000,000) years old. So any fossils found there should be that old, or tourists!

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