Year 4 Science

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fish fossil

Have you ever made a sandcastle? Did you fill a bucket with wet sand and then turn it upside down to make a tower? You used the bucket as a mould. That tells you something about how fossils were made. They are made of rock, not just sand. The sandcastle lasts only until the sea comes in over it. A fossil lasts a very long time, millions of years in fact, but it takes a long time for the rock to form.

Living things have soft parts, which decay quickly after they die, and hard parts, which last longer. You know that there are hard bones under your softer skin, muscles and blood vessels. If an ancient body is dug up it's usually just the skeleton and teeth that have survived. Similarly, the shells of snails and limpets last longer than the living creatures inside them. When these creatures die, sand and mud can cover the shell and start the long, slow process of turning into rock or stone. The shell is a mould, like the bucket for the sandcastle. In time, the sand and mud turn into rock that is formed around the shell and takes on its shape. This is a fossil. It is like a three-dimensional picture in stone of something that was alive before the rock formed.


Most fossils are small. Look on a pebbly beach (although some beaches are better than others). On beaches along the Jurassic Coast in Dorset you have a good chance of finding a stone with a print of a broken sea shell from long, long ago. You have a small chance of finding a whole shell fossil, a dinosaur bone or even a whole dinosaur! The animals are extinct but these fossils help us learn about them.

Plants can become fossils too. Coal is a plant fossil, for example. Amber is particularly beautiful, formed when sticky resin went solid and eventually hardened into stone. Sometimes the resin caught an insect, which was then preserved for thousands and thousands of years.

This activity is adapted from pages 297-298 of What Your Year 4 Child Needs to Know, which can be purchased here. Click below to see the related activities.

science owl
science owl