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4.6 billion years ago
What is when do scientists believe Earth's history started?
The idea that Earth's history was shaped by sudden disasters.
What is catastrophism?
James Hutton
Geologic processes today are similar to those in the past.
What is the principle of uniformitarianism?
The order in which geologic events occurred.
What does relative-age dating help scientists determine?
The age of rocks compared to other nearby rocks.
What does relative age refer to?
The oldest rocks are on the bottom.
What is according ot the principle of superposition, in undisturbed rock layers?
Most rock-forming materials are deposited in horizontal layers.
What is the principle of original horizontality state?
Sediments are deposited in large, flat sheets.
What does lateral continuity mean?
The feature that is cut across is older.
What is according to cross-cutting relationships, if one geologic features cut across another?
A piece of older rock that becomes part of a new rock.
What is an inclusion?
The preserved remains or evidence of ancient living things.
What are fossils?
What are tiny fossils that can only be seen with a microscope?
Simple organisms appear in older layers.
What pattern did early geologists notice about fossils in rock layers?
What are the times when mass extinction happens?
What ancient environments were like.
What are how do scientists use fossils?
Wind and rain weather and erode them.
What happens to rocks when they are exposed at Earth's surface?
A surface where rock has eroded away, creating a gap in the rock record.
What is unconformity?
Horizontal sedimentary rock overlies eroded horizontal sedimentary rock
What is when does disconformity occur?
Horizontal layers are deposited on tilted, eroded layers
What is when angular unconformity form?
Sedimentary rock overlies igneous or metamorphic rock.
What is when nonconformity occur?
Matching rocks and fossils from separate locations.
What is correlation in geology?
What are index fossils?
Rock or sediment layers are used as markers to correlate rock layers.
What are key beds?
A model of Earth's history from origin to present.
What is the geologic time scale?