The idea that the natural processes happening today (like weathering and erosion) are the same ones that happened in the past. Basically, "the present is the key to the past."

The remains or traces of an organism that lived long ago, usually preserved in sedimentary rock.

A fossilized structure that formed in sedimentary rock by animal activity on or within soft sediment (like footprints, burrows, or dung).

The long-term weather patterns in a specific area over a long period.

A long cylinder of ice drilled out of a glacier or ice sheet. Scientists use these to study the history of Earth’s atmosphere and climate.

Determining whether an object or event is older or younger than other objects or events. It doesn't give an exact age in years.

The principle that states that in undisturbed rock layers, younger rocks lie above older rocks.

A "gap" in the geologic record. It’s a surface where rock layers are missing because they were eroded away or because sediment was never deposited there.

An ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom.

Measuring the age of an object or event in years.

The process in which a radioactive isotope (unstable atom) breaks down into a stable isotope of the same element or another element.

The time needed for half of a sample of a radioactive substance to undergo radioactive decay to form daughter isotopes.

he method used to find the absolute age of a sample by determining the relative percentages of a radioactive parent isotope and a stable daughter isotope.

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Earth's History

Term	Definition
Uniformitarianism	The idea that the natural processes happening today (like weathering and erosion) are the same ones that happened in the past. Basically, "the present is the key to the past."
Fossil	The remains or traces of an organism that lived long ago, usually preserved in sedimentary rock.
Trace Fossil	A fossilized structure that formed in sedimentary rock by animal activity on or within soft sediment (like footprints, burrows, or dung).
Climate	The long-term weather patterns in a specific area over a long period.
Ice Core	A long cylinder of ice drilled out of a glacier or ice sheet. Scientists use these to study the history of Earth’s atmosphere and climate.
Relative Dating	Determining whether an object or event is older or younger than other objects or events. It doesn't give an exact age in years.
Superposition	The principle that states that in undisturbed rock layers, younger rocks lie above older rocks.
Unconformity	A "gap" in the geologic record. It’s a surface where rock layers are missing because they were eroded away or because sediment was never deposited there.
Geologic Column	An ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom.
Absolute Dating	Measuring the age of an object or event in years.
Radioactive Decay	The process in which a radioactive isotope (unstable atom) breaks down into a stable isotope of the same element or another element.
Half-life	The time needed for half of a sample of a radioactive substance to undergo radioactive decay to form daughter isotopes.
Radiometric Dating	he method used to find the absolute age of a sample by determining the relative percentages of a radioactive parent isotope and a stable daughter isotope.

Created by: Summer Cali Taylor Hudson

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