What is sedimentation?

The Blue Lias. A cliff made out of layers of mud, sand and limestone near Lyme Regis, UK. (MichaelMaggs, Wikimedia)

The Blue Lias. A cliff made out of layers of mud, sand and limestone near Lyme Regis, UK. (MichaelMaggs, Wikimedia)

Sedimentation is very important. Without it we wouldn’t have any dinosaur fossils. It is the building up of layers of small particles like sand or mud. The easiest place to see this is the beach. A beach is made up of lots of sand which have been deposited, or left behind, by the sea.

Sand and mud come from inland. Rivers erode them from the land and bring them towards the sea. As the water slows, it can’t carry as much and so sand and mud are dropped. The bigger the grain of sand, the sooner it is dropped.

If you look at a cliff, you will often see layers which make the cliff look like a layer cake. These layers are caused by sedimentation. Over a long period of time, the grains of sand and mud build up and up, forming the layers.

Fossils are found in these layers. The quicker bones are buried, the more chance they will be saved from scavenging animals and damage by weather.

The sea, rivers and lakes are the best depositors of sand and mud and dinosaurs are found where there used to be a sea, lake or river. But big glaciers also carry grains and the air can also carry very small grains.

A land-slide, where mud and rock fall down a mountain of a sand dune can also save the bones of a dinosaur. One famous fossil called ‘The Fighting Dinosaurs’ is two dinosaurs entwined as though they are fighting. Palaeontologists think that the Velociraptor was hunting the other dinosaur, Protoceratops when a sand dune collapsed on both, killing them and preserving their bones.  

What is Inheritance?


A diagram showing how children inherit blood type from their parents.

Inheritance is why you look similar to you mum or dad. People’s bodies have characteristics, like the shape of their nose or the colour of their eyes, and parents pass on these characteristics to their children, this is inheritance.

We are made of cells like a building is made of bricks. Our cells are told what to do by DNA. DNA is the boss and tells the cells how to make a human body. All of us are made up of DNA from both our mum and dads so we inherit orders on how to build a body from both of them that is why we have characteristics from both our parents.

People look like people. Every person is unique but they have far more in common than they are different. This is because we are all related and we have all inherited characteristics from our ancestors.

We share an ancestor with a monkey but that ancestor lived a very long time ago so we look more different from monkeys. Even so, people and monkeys still have a lot in common. We both have two legs, two eyes, two hands and many other things. generally, the closer related we are to another species, the more like them we look.

Watch this video to find out more about DNA, the molecule which we inherit from our parents

What is Evolution?

A cartoon of Darwin as an Ape, his theories on evolution were controversal when he was alive. (Wikimedia

A cartoon of Darwin as an ape, his theories on evolution were controversal when he was alive. (Wikimedia)

Evolution is a theory, an idea with lots of evidence. It explains why animals and plants are so good at surviving in their environments, the places where they live. What it means is that a species changes over time and can even split in two new species.

The theory of evolution was developed by Charles Darwin back in 1859. He said that evolution worked through natural selection. Natural selection means that some individuals in a species are better at surviving than others and will have more children.

Rabbit live all over, and have dark fur. But in a place where it snows a lot, white fur would be an advantage. A white furred rabbit would be harder to see and is more likely to survive and have children. These children will inherit its mum or dad’s white fur. Eventually all the rabbits living in the cold place will have white fur.

This is called ‘survival of the fittest’ because animals which are best able to survive also fit better in their homes, like a white rabbit fits better in a cold country.

Evolution also explains how one species can become two, like with the rabbits. We call this Speciation. The white rabbits are better fits where it snows but dark brown rabbits fit better where it snows less. With time, the different rabbits will become different species, both living in their own, separate environment.

Evolution says that all living things are related. This means that if will go back far enough in time, all animals, all plants and every other living thing, had one ancestor. Evolution led to that one species becoming many more until today when we have millions and millions.

Some animals are more closely related than others. The more closely related animals are, the more they look and act alike. Swans and geese look and act so similar because they are closely related. A sparrow looks very different to a swan but both still have beaks, feathers and can fly so are related but less closely than the swan is to the goose.

we look very different to a swan or a sparrow but we do have similarities. We both have two eyes, both have two legs, two arms (adapted to wings in a bird), one head, one heart, a nose and ears. We share all of these things and more with birds so, although we are very different, we are also related to birds.

Evolution is an important part of palaeontology. Many of the extinct animals found look like they have bits of different animals stuck to them. Many fossil birds are found with teeth. This is because birds evolved from Dinosaurs which do have teeth. Eventually birds lost their teeth and now no living species has them.

So evolution means we share a history with all the animals around us but also all the animals that are extinct. It means we are a part of nature and not better than it or above it. And it means that we should treasure those connections with nature and better protect them from our own, sometimes destructive, ways.

Watch this video to find out more

What is a species?

Drawing of some dog breeds.

Drawing of some dog breeds.

A species is a group of animals that all look similar and can have babies with any other member of that species. Humans are a species called Homo sapiens. We are one species because we all look very similar and can have children with each other.

But the members of a species can look very different from each other. Dogs are all one species called Canis lupus. This species includes every dog breed, from great danes to poodles and even wolves.

Cats, on the other hand, are a different species to dogs because a cat cannot have a baby with a dog.

What is a fossil?


A dinosaur fossil (Mike Beauregard, Wikimedia

A dinosaur fossil (Mike Beauregard, Wikimedia)

A fossil is evidence of life from far back in the past. There are many types of fossil but the best known is bone. Bone is hard and strong and is often the only part of an animal to survive years after an animal has died. If those bones are buried, there is a chance that someone may find it millions of years later.

Other types of fossil include shells of sea animals like sea snails or oysters and clams. Plants can also be preserved and, occasionally, soft tissue like muscles, but these are very rare.

what is preservation?

A group of bones being dug up by palaeontologists

A group of bones being dug up by palaeontologists

Preservation simply means that bones have survived by being buried underground ever since the animal died. It can happen in many ways and sometimes the fossil can be damaged but if it is there, it is preserved.

Preservation is more likely if the bones are buried very quickly. This is because other animals can damage them, as can the weather. Even if the bones are buried they may not be preserved.

Sometimes there can be a lot of acid in the ground and this can dissolve the bone or shell and leaves nothing behind. Sometimes a shell may dissolve away but something else fills the gap and so the fossil survives and looks the same. This is called precipitation which is the growth of crystals. Its these crystals than fill the spaces left after the fossil had dissolved.

Precipitation can also fill the gaps in bones. Bones are not all solid and there are lots of small holes through them. Crystals may grow in these gaps and this makes the fossil look and feel like a rock.

When soft parts survive

Bones and shells are usually all that is preserved but sometimes other parts survive. Soft parts of bodies are usually destroyed by bacteria which use the soft parts as food. Soft parts include skin, organs and blood. Animals preserved in ice may still have these soft parts because it is too cold for the bacteria. This is why we have soft bits of woolly mammoths.

If there is no oxygen, bacteria can’t survive either. Water has oxygen in it but sometimes all the oxygen is used up by bacteria. Sometimes lakes lose all their oxygen and so soft parts can be preserved. Lakes, which are long gone, are where insect fossils can be found if those lakes had no oxygen in them when the insects died.

Another way soft parts can survive is if there is no water as bacteria need water too. Soft parts can survive thousands of years in dry deserts but as soon as it rains, bacteria start to destroy the soft parts. So fossils are rarely preserved in this way.

What is the Mesozoic?


A diagram showing the different periods of the Mesozoic and when they started and finished.

The Mesozoic era is a length of time. It started 248 million years ago and ended 65 million years ago. This very long period of time is called an era.

The word ‘Mesozoic’ means middle animals and the types of animals were very different to what came before or after. The middle animals were dominated by dinosaurs, pterosaurs, pliosaurs, plesiosaurs and many other types of animals.

The Mesozoic is divided into three sections called periods:

  • The Triassic Period lasted from 248 to 208 million years ago
  • The Jurassic Period lasted from 208 to 146 million years ago
  • The Cretaceous Period lasted from 146 to 65 million years ago

Although the Mesozoic is often known as the age of dinosaurs, it wasn’t until the Jurassic that dinosaurs became the most common large animals. For most of the Triassic, they were small and uncommon.


Each of the periods had different types of animals than the others. The Triassic is when dinosaurs and mammals are thought to have evolved, as did the pterosaurs and ichthyosaurs.


The Jurassic was the time of the long-necked, or sauropod, dinosaurs and is the time when birds are first seen.


The Cretaceous has some of the most famous dinosaurs like Tyrannosaurus rex and Triceratops but it is also when flowers and flowering plants first evolved. The Cretaceous is also when many of the big dinosaurs died out but dinosaurs live on now as birds.

65 million years ago, a meteor smashed into earth. The sky turned black from all the dust thrown into the sky and, as the dust came back down, it formed black lines. these black lines mark the end of the Cretaceous and the extinction of non-bird dinosaurs.

The End of the Mesozoic marked the beginning of the Cenozoic which is the era we are in now and is often called the age of mammals.

What does extinction mean?


Some animals that have gone extinct. Clockwise starting from top left: Tyrannosaurus rex, Tasmanian tiger, Steller's sea cow, Golden toad, Passenger pigeon and Dodo.

Some animals that have gone extinct. Clockwise starting from top left: Tyrannosaurus rex, Tasmanian tiger, Steller’s sea cow, Golden toad, Passenger pigeon and Dodo.

When every single member of a species dies and none are left alive, then that animal has gone extinct. Extinctions can happen for many reasons but recently people have been a major cause.

Over hunting can led to extinction as can diseases, climate change or habitat loss which is when animal’s homes are destroyed.

In the past, there have been very large extinctions where many species have gone extinct together. This is called an extinction event. One of these events wiped out the dinosaurs.

65 million years ago, all dinosaurs (except birds) went extinct as did many other types of plants and animals. It was at the end of the Cretaceous period and scientists think that it was caused by a big meteor.

A meteor is a big rock that comes from space. When this meteor hit Earth, there was a massive explosion and dust was blown into the sky. Scientists think this dust changed the Earths weather and made it very cold and dark. Animals found it hard to survive and many died. Dinosaurs were just some of the animals that went extinct.