states that geologic processes that happened in the past can be explained by current geologic processes.

the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock. Fossils may be skeletons or body parts, shells, burrows, or ancient Coral reef.

is a fossilized structure that formed in sedimentary rock by animal activity on or in soft sediment. One type of trace fossil can be tracks, they are foot prints made by animals and soft sediment that later become hard rock.

scientist use rocks and fossils to determine whether an object or event is older or younger than other objects or events. This does not give scientists a rocks age in years, only what rock layer is older or younger than another rock layer.

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

a break in the geologic record that is made when rock layers are eroded or when sediment is not deposited for a long period of time. When scientists must question if the missing layer was simply never present or if it was removed.

an ordered arrangement of rock layers that is based on the relative ages of the rocks, with the oldest rocks at the bottom of the column. It is made by piecing together different rock sequences from different areas.

is the determining the actual age of an event or object in years. One example of absolute dating is using radioactive isotopes.

the breakdown of a radioactive isotope into a stable isotope of the same element or of another element Radioactive decay for many isotopes happens when a neutron is converted to a proton, with the release of an electron.

the time needed for half of a sample of a radioactive substance to undergo radioactive decay to form daughter isotopes; always given in units of time.

finding 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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Geological Time

Vocabulary

Term	Definition
Uniformitarianism	states that geologic processes that happened in the past can be explained by current geologic processes.
Fossils	the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock. Fossils may be skeletons or body parts, shells, burrows, or ancient Coral reef.
Trace fossil	is a fossilized structure that formed in sedimentary rock by animal activity on or in soft sediment. One type of trace fossil can be tracks, they are foot prints made by animals and soft sediment that later become hard rock.
Relative dating	scientist use rocks and fossils to determine whether an object or event is older or younger than other objects or events. This does not give scientists a rocks age in years, only what rock layer is older or younger than another rock layer.
Superposition	the principle that states that younger rocks lie above older rocks if the layers have not been disturbed.
Unconformity	a break in the geologic record that is made when rock layers are eroded or when sediment is not deposited for a long period of time. When scientists must question if the missing layer was simply never present or if it was removed.
Geologic column	an ordered arrangement of rock layers that is based on the relative ages of the rocks, with the oldest rocks at the bottom of the column. It is made by piecing together different rock sequences from different areas.
Absolute dating	is the determining the actual age of an event or object in years. One example of absolute dating is using radioactive isotopes.
Radioactive decay	the breakdown of a radioactive isotope into a stable isotope of the same element or of another element Radioactive decay for many isotopes happens when a neutron is converted to a proton, with the release of an electron.
Half- life	the time needed for half of a sample of a radioactive substance to undergo radioactive decay to form daughter isotopes; always given in units of time.
Radiometric dating	finding the absolute age of a sample by determining the relative percentages of a radioactive parent isotope and a stable daughter isotope

Created by: Payneaa

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