This week we will be learning more about fossils. Watch the video to find out a little more about the different types of fossils and they way in which they are formed.
There are two main types of fossil:
- Body Fossils are the fossilised remains of an animal or plant, like bones, shells and leaves. These can include mould and cast fossils, like most of the fossilised dinosaur skeletons and big bones we see. They can include replacement fossils, like petrified wood where the original organism decays but the space where it used to be is replaced by minerals. They can be whole body fossils like mammoths caught in ice, or insects trapped in amber.
- Trace Fossils are fossilised remains that show the activity of an animal. These are not the body parts of an animal but they show how the animal lived. These include footprints, tracks and fossilised poo.
Fossils are the remains of once living animals or plants. People have been finding fossils in rocks for thousands of years, but until quite recently they didn't understand what they were.
Today we recognise that the fossils we find in rocks represent the ancestors of the animals and plants that are alive today.
Not many plants and animals are lucky enough be turned into fossils.
When an animal or plant dies its remains usually rot away to nothing. Sometimes though, when the conditions are just right and its remains can be buried quickly, it may be fossilised. There are several different ways fossils are formed. Here we go through the five steps of fossilisation to make a typical cast fossil.
- An animal dies, its skeleton settles on the sea floor and is buried by mud and sediment. The sea floor is an ideal place for fossilisation, which explains why many fossils are marine (from animals that lived in the sea). Land animals may die and be swept out to sea to be buried in the same way.
- The sediment surrounding the skeleton thickens and begins to turn to stone.
The skeleton continues to be buried as more layers are added to the surface of the sea floor. As the sea floor sinks, pressure increases in the lower layers of sediment and it turns it into hard rock.
- The skeleton dissolves and a mould is formed.
Now it is deeply buried and surrounded by stone, the skeleton is dissolved by the water in the ground. This leaves a or hole in the shape of the original skeleton. This hole is known as a natural mould.
- Minerals crystallise inside the mould.
Water enters the mould, and fills the cavity. The minerals dissolved in the water start to form crystals in the mould. This is called a cast and it has the same shape as the original skeleton.
- The fossil is exposed on the Earth's surface.
Millions of years later, the rock surrounding the skeleton rises to the Earth's surface (this happens during mountain building, earthquakes and other earth processes). The rock is worn away by wind and rain, and the fossil is now exposed, waiting to be found!
If you have a printer, you can make your own Fossilisation Zig Zag book using this template. If you don't have a printers, you can still make a zig zag book by folding paper and describing each stage in the formation of a fossil.
Now have some fun playing this fossilisation board game! You will need a dice and some counters and a copy of the gameboard.
Fossils give us information about how animals and plants lived in the past.
Once people began to recognise that some fossils looked like living animals and plants, they gradually began to understand what they were. They realised they were actually the ancestors of today's plants and animals.
Some fossils are easy to identify and look like plants and animals alive today.
While we can easily recognise and identify some fossils, many fossils represent animals that no longer exist on Earth. We only know about extinct groups like dinosaurs, ammonites and trilobites through fossils.
Some animals and plant are only known to us as fossils.
By studying the fossil record we can tell how long life has existed on Earth, and how different plants and animals are related to each other. Often we can work out how and where they lived, and use this information to find out about ancient environments.
This week we are going to try using the continuous line drawing technique to make some drawings of fossils.
You can find out more about continuous line drawing in this video.
Here are some fossils you might like to try drawing using the continuous line technique.