Change Over Time

remains of ancient plants and animals fossil remains of ancient plants and animals

natural selection slow process of organisms that are best suited in their environment survive and reproduce

adaptation a structure or behavior that helps an organism survive in its environment

common ancestor the shared ancestor of new, different species that came from one population

the dying out of a whole species extinction the dying out of a whole species

a large-scale dying out of many species in a short period of time mass extinction a large-scale dying out of many species in a short period of time

a group of organisms that look alike and can reproduce offspring species a group of organisms that look alike and can reproduce offspring

geologic time scale a chart that shows earth’s history and divides it into eras and periods

mold fossil a fossil made when an organism decays inside a rock and leaves it’s shape in the rock

tree sap that hardens, often with an insect inside amber tree sap that hardens, often with an insect inside

cast fossil a fossil made when minerals fill a hole left when an organism decayed; a cast fossil is a model of the organism.

petrification Fossil made when minerals replace the bones or organic matter left by an organism; internal bone structure can be seen