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Earth's History

Science

Earth's History Chapter Video

Earth's History Chapter Video

continental drift

the hypothesis that all the continents are moving very slowly across Earth’s surface
continental drift Simple Definition

geologic time scale

a timeline of Earth's history based on major changes
geologic time scale Simple Definition

half-life

the time it takes for half the atoms of a radioactive isotope to decay
half-life Simple Definition

index fossil

a fossil from an organism that existed for a short time, it is used to determine the age of other fossils
index fossil Simple Definition

law of superposition

the oldest rock layers are at the bottom and youngest are at the top
law of superposition Simple Definition

plate tectonics

the theory that Earth's crust is made of moving plates
plate tectonics Simple Definition

radioactive decay

the breakdown of an unstable atomic nucleus, this releases particles and energy
radioactive decay Simple Definition

relative age

the age of one object or event compared to another
relative age Simple Definition

relative dating

a method of comparing fossils or rocks to determine which is older
relative dating Simple Definition

sedimentary rock

a rock that forms when sediment is pressed and cemented together
sedimentary rock Simple Definition

trace fossil

a fossil formed in soft sedimentary rock, like a footprint
trace fossil Simple Definition

uniformitarianism

the theory that geologic processes are the same today as they were in the past
uniformitarianism Simple Definition

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