Earth History Vocabulary Uniformitarianism The idea that the

Earth History Vocabulary

Uniformitarianism The idea that the same geologic processes shaping the Earth today have been at work throughout Earth’s history.

Catastrophism The principle that states that all geologic change occurs suddenly.

Paleontology The scientific study of fossils.

Superposition A principle that states that younger rocks lie above older rocks if the layers have not been disturbed.

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

Geologic Column An arrangement of rock layers in which the oldest rocks are at the bottom.

Absolute Dating Any method of measuring the age of an object or event in years

Relative Dating Any method of determining whether an event or object is older or younger than other objects or events.

Radioactive Dating Also known as radiometric dating is a method of determining the age of an object by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.

Fossil The remains or physical evidence of an organism preserved by geological processes

Trace Fossil A fossilized mark that is formed in soft sediment by the movement of an animal

Mold A mark or cavity made in a sedimentary surface by a shell or other body

Cast A type of fossil that forms when sediments fill in the cavity left by a decomposed organism

Index Fossil A fossil that is found in the rock layers of only one geologic time age and is used to establish the age of rock layers

Extinction The death of every member of a species

Geologic Time Scale A scale that divides the earth’s 4. 6 billion year history into distinct intervals

Eon The largest division of geologic time

Era A unit of geologic time that includes 2 or more periods

Period A unit of geologic time in which eras are divided.

Epoch A subdivision of a geologic period.

Ice Cores A sample of ice and snow that contain trapped atmospheric gasses and particles to show scientists the composition of the atmosphere at a particular time in the past.

Fault A break in the Earth’s crust along which blocks of the crust slide relative to one another.