Unit 9 Geologic Time and Fossils

fossil

remain or trace of an organism that once lived

body fossil

actual remains of an organism, such as bones, teeth, or shells

trace fossil

indirect evidence of life, like footprints, burrows, and feces

mold fossil

an imprint left in rock

cast fossil

replica of the original organism

petrified fossil

fossils turned into stone

amber fossil

fossilized tree resin containing a trapped organism

eon

the largest period of time, Earth had four

eras

major intervals of time, starting and ending with major changes

periods

smaller divisions of time within eras

epochs

smaller divisions of time within periods

rock strata

horizontal layers of rock that form on top of one another

index fossil

remains of an organism that lived for only a short period of time

Law of Superposition

in any stack of undisturbed rock layers, the newest rocks are on the top and the oldest rock are on the bottom

magma intrusion

when magma rises from the Earth's mantle and intrudes into existing rock layers