Sedimentary rocks begin forming when existing rocks are worn away by wind and rain in a process called weathering. Weathering breaks rock into smaller pieces called sediment. Erosion is the removal and movement of sediment. Weathering and erosion happen slowly, over thousands and even millions of years. Eventually, layers of sediment are deposited on top of one another and pressed together. Sedimentary rock is formed when sediment sticks together after liquid is squeezed out. Sometimes, fossils get trapped between sediment layers. The sediment of sedimentary rocks can range in size from a grain of sand to a shell or pebble. The name of the rock that’s created depends on the sediment that it’s made of. For example, shale is made of clay. Conglomerate is made of coarse sediment the size of small pebbles. The sediments of limestone are small shells.

Which of the following is an example of erosion?

A
Wind breaking down an existing rock into smaller pieces.

B
Layers of sediment pressed and sticking together.

C
Small shells being moved by water to the shore.

D
Animal fossils getting trapped between sediment layers.