Remains, imprints, or traces of prehistoric organisms.
Permineralized remains:
Fossils in which the spaces inside are filled with minerals from groundwater.
Carbon film:
A thin film of carbon residue left, that forms a silhouette of the original organisms.
Mold:
A type of body fossil that forms in rock when an organism is buried, decays or dissolves and leaves a cavity in rock.
Cast:
Type of fossil that forms when sediments or water enter the cavity, form new rock, and produce a copy of the original object.
Index fossil:
Remains of species that existed on Earth for relatively short periods of time, were abundant and were widespread geographically.
Principle of superposition:
States that in undisturbed rock layers, the oldest rocks are on the bottom and the rock become progressively younger toward the top.
Relative age:
The age of something compared with other things.
Unconformity:
Gaps in rock sequences in the rock layer due to erosion or periods without any deposition.
Absolute age:
The age, in years, of a rock or other object.
Radioactive decay:
Process in which some isotopes break down into other isotopes and particles.
Half-life:
Time it takes for half of the atoms in the isotope to decay.
Radiometric dating:
Process used to calculate the absolute age of rock by measuring the ratio of parent isotope to daughter product in a mineral and knowing the half life of the parent.
Uniformitarianism:
Principle stating that Earth processes occuring today are similar to those that occured in the past.