Vocabulary Chapter 19


Chapter 19 vocabulary

Fossilization- the process of fossilizing a plant or animal that existed in some earlier age

Index Fossil- a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found.

Geologic Time Scale- scale used by paleontologists to represent evolutionary time

Key bed- a thin, widespread, easily recognized sedimentary layer that can be used for correlation.

Law of superposition- The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it

relative age- the age of something compared with other things

stratigraphy- the natural layering of cultural deposits and natural soil layers that build up on a site over a long period of time. These soil layers will often be different in color and texture from each other. The most recent artifacts and features are found closer to the surface, and the oldest deposits are at the bottom.


a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time

absolute age-

the age of a rock given as the number of years since the rock formed

carbon-14 dating

Process of estimating age of once living material by measuring the amount of radioactive isotope of carbon present in material.


the time required for one half of the atoms of a radioisotope to emit radiation an decay products


one of two or more atoms with the same atomic number but with different numbers of neutrons.

radioactive decay-

the spontaneous disintegration of a radioactive substance along with the emission of ionizing radiation.

radiometric dating-

the process of measuring the absolute age of geologic material by measuring the concentrations of radioactive isotopes and their decay products.


the mass of air surrounding the Earth.

nuclear fusion-

a nuclear reaction in which nuclei combine to form more massive nuclei with the simultaneous release of energy.

water vapor-

water in the form of a gas.