Geologic Change Over Time

Uniformitarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes

Fossil

The preserved remains or traces of an organism that lived in the past

trace fossil

the preserved evidence of the activity of an organism

climate

Overall weather in an area over a long period of time

ice cores

method for studying climate change by drilling cores in ice caps and glaciers that have build up over thousands of years

relative age dating

a way to describe the age of one object or event compared to another object or event

absolute age dating

method that enables scientists to determine the actual age of certain rocks and other objects

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 are eroded or when sediment is not deposited for a long period of time.

geologic column

an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest

radioactive decay

The breakdown of a radioactive element, releasing particles and energy

index fossil

fossils of widely distributed organisms that lived during only one short period

fossil record

information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived

geologic column

an arrangement of rock layers in which the oldest rocks are at the bottom

intrusion

An igneous rock layer formed when magma hardens beneath Earth's surface.

Extrusion

An igneous rock layer formed when lava flows onto Earth's surface and hardens.

law of crosscutting relationships

the principle that a fault or body of rock is younger than any other body of rock that it cuts through