Geologists are scientists who study the earth. they search through rivers, mountains, and caves for clues about how and when the earth was formed. some of these clues are millions of years old. geologists study clues like caves and fossils to find out more about the earth.
caves are natural holes or tunnels that go underground. a geologist would study a cave to find out several things. first, what made the tunnel? some caves are made by water or lava. second, what kind of rock is the cave made of? caves can be made out of many different types of rock.
sometimes, geologists find fossils buried under the ground. a fossil is a bone, shell, or footprint left from ancient animals or people. fossils are good clues for geologists to study. if a geologist finds the fossil of an ancient fish in a rock, he or she can guess that a river or ocean used to flow nearby.

which is the best summary of the selection?
geologists are scientists who study the earth. they study important clues like caves and fossils.
a fossil is something left by a creature that used to be alive. some fossils were left by ancient fish.
caves are natural holes that go underground. geologists study caves to learn how they were formed.
geologists are scientists who study caves. caves can be made out of many different types of rock.