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 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.

Tarbosaurus baatar

Skeleton of Tarbosaurus (Eduard Solà, Wikiamedia)

Skeleton of Tarbosaurus (Eduard Solà, Wikiamedia)

Tarbosaurus was the king in the Late Cretaceous of Mongolia just as its close relative Tyrannosaurus was king in North America. Although slightly smaller than T.rex, Tarbosaurus was a big bad predator. Smart dinosaurs would avoid this two-legged killing machine.

Discovery: It was named in 1955

Height: 5.6m

Length: 1012m

Weight: 7000kg or a little less.

Where it lived: Found in Mongolia and China.

When it lived: it lived 75-70 million years ago in the Late Cretaceous.

What it ate: A meat eater, like T.rex, it would eat anything it could fit in its mouth. (they may have even been cannibals.)

Weapon of choice: a massive head with rows of teeth up to 20cm long.

Weakness: T.rex had tiny hands with just two claws; Tarbosaurus had even smaller hands that were even more useless.

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.