Page 21 - York Global Science 4 - Earth & Space

Earth and Space Science

Let’s Learn
Let’s Learn

Sedimentary rocks are made in layers. Particles of sand or mud settle out
of water. They get pushed together by other particles added slowly from the

water above. After a long time, they change into rock.

layer 3

layer 2

layer 1

In this picture:
• Layer 1 was made fi rst. Layer 1 is the oldest.

• Then layer 2 was made on top.

• Layer 3 was made last. Layer 3 is the youngest rock layer.
However, we do not always find the oldest rocks at the bottom, and the
youngest rocks at the top. The Earth’s surface is made up of plates that

move. The plates only move very slowly. But over a long time they can pull
away from each other or push together. Look again at the picture in Let’s
Start. These rock layers folded when they pushed together. The oldest rocks

are not always at the bottom now.
Sometimes the movement of the plates can make an earthquake happen.
This can make rock layers break in some places. It can change which layers

are closer to the surface. Sometimes magma escapes as lava from the
volcano when the plates move. The magma turns into igneous rock.

A fossil can show if the rock layers changed. We know that some living
things, like the dinosaurs, were only on Earth at one time in history. The
fossils in a rock layer can help us decide how old it is. This can show
whether the order of the layers has changed. For example, older rock layers
could be moved nearer the top by an Earth event.

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