Rocks shape the land
If you climb a hill and look around, you can probably see for many kilometres in any direction. As you look around, you may see other hills. Some may be higher than the one you are standing on. Perhaps some others are smaller. Between the hills you would see valleys. Their sides may be steep or just gentle slopes. The shape of the land is made by the rocks underneath it.

Although you cannot see it, there are changes taking place in the landscape. If you took a photograph of your view and came back again in thirty years time, you would probably not see much difference. Perhaps, if a river was in your view, it may have become wider or changed its course a little. The hills and valleys, however, would probably look the same. If you could travel back in time ten thousand years the view would have looked very different. The valleys would not have been so deep and the river might have been just a stream.

The way the land changes is due to its rocks. They are all worn away by the weather. Some rocks are softer than others. They are more easily broken up by the weather. Their rocky pieces are carried away by the wind and by water. The hollows that they leave become the valleys in the countryside. The hills are made of harder, more weather-resistant rock but in time they will become smaller too.

Why can you get hard rock and soft rock in the same place?
The hard and soft rocks formed at different times. When most rocks form, they form layers. When lava flows away from a volcano, it forms a layer over the ground. This layer cools to form a layer of basalt. Later the ground may be flooded by a sea. When this happens, the shells of tiny sea creatures may settle on the basalt and form a layer of chalk. The basalt is a hard rock. The chalk is a soft rock.

Do the layers of rock take the same time to form?
No. The basalt layer only takes a few years to cool down and form. The chalk may take millions of years. Most layers of rocks are formed from sedimentary rocks and all these layers take a long time to form. Some layers are thicker than others so they will take longer to form than thinner layers.

Are layers of rock forming today?
Yes. Wherever lava flows out of a volcano it will form a layer of rock. The ash, which settles after a volcano erupts, will also form a layer of rock. At the mouths of rivers, layers of rock are building up which will turn to stone in millions of years. Chalk may be forming from the shells of tiny sea creatures that have fallen onto the ocean floor. A special type of limestone called oolitic limestone is forming from tiny pieces of shell and sand on the sea floor near Florida.

Why are some layers tilted?
When a layer forms it is usually horizontal. It will remain horizontal unless the crust it is in receives a push. The rocky crust of the Earth is divided up into huge slabs that are thousands of kilometres across. The slabs of rock are called plates and they move very slowly. When one plate pushes against another, it pushes on the layers of rock. This makes them bend and fold. You can see how this happens by performing a little experiment with Plasticine. Take three strips of Plasticine. Lay one on top of another to make three layers. Now push on the ends of the Plasticine and see how the layers bend and fold.

Can the wind break down rock?
Yes. It can do it in two ways. First it can blow loose particles from the rock surface. Secondly it can blow sand, grit and dust at the rock. When they hit the surface at speed they can chip away bits of the rock. In deserts, the bottom of large rocks may be hit so often by low flying sand that it wears away. This makes the rock look as if it is standing on a pedestal. Boulders in the desert are blasted so much by the sand that they are worn into rounded shapes with smooth surfaces.

Can the sea break down rock?
Yes, it can. The waves crash against the rocks in a cliff and wear them away. If the coast has hard rocks and soft rocks the sea will wear away the soft rocks more than the hard rocks. As the soft rocks wear away the sea goes further inland. In time it may make a small circular bay called a cove. They make a safe mooring for boats and in the past were used as a hiding place by pirates.

What happens when the sea breaks down hard rocks?
As hard rocks take a long time to wear down, they make the headlands on a coast. The softer rocks close by wear away to make bays. The sea may bash a hole in a headland and make a cave. In time the sea may punch its way through the headland and make an archway known as a sea arch. As the sea continues to bash at the walls of the arch it eventually makes the top of the arch break away. This leaves a tall rocky column called a sea stack.