FOSSILS

Fossil

Preserved remains or traces of ancient living organisms found in rocks

Sedimentary rock

Type of rock formed from layers of sediment where fossils are commonly found

Mold fossil

Impression left in rock after an organism decays

Cast fossil

Fossil formed when minerals fill a mold and harden into the shape of the organism

Trace fossil

Evidence of organism activity such as footprints or burrows

Fossilization

Process where remains of organisms are preserved over long periods of time

Relative dating

Method of determining fossil age by comparing rock layers

Absolute dating

Method of determining exact age of fossils using radioactive decay

Carbon dating

Technique used to determine age of once-living organisms using carbon-14

Index fossil

Fossil of a widespread species used to determine the age of rock layers

Petrified fossil

Fossil where organic material is replaced by minerals over time

Half-life

Time it takes for half of a radioactive substance to decay

Stratification

Formation of layers of sedimentary rock over time

Geologic time scale

System that organizes Earth’s history into eras, periods, and epochs

Fossil record

Collection of all fossils that shows the history of life on Earth

Paleontology

Scientific study of fossils and ancient life forms

Radiometric dating

Method of dating fossils using radioactive isotope decay