For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away
by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.

sandstone

limestone

shale

conglomerate

gypsum