The majority of geological data comes from research on solid Earth materials. These typically fall into one of two categories: rock and unlithified material. Meteorites and other extra-terrestrial natural materials are also

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Plate tectonics
In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost

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The geological time scale encompasses the history of the Earth. It is bracketed at the earliest by the dates of the first Solar System material at 4.567 Ga (or 4.567 billion years ago) and the formation of the Earth at 4.54 Ga (4.54 billion years), which is the beginning of the

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The geology of an area changes through time as rock units are deposited and inserted, and deformational processes change their shapes and locations.
Rock units are first emplaced either by deposition onto the surface or intrusion into the

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Geologists use a number of fields, laboratory, and numerical modeling methods to decipher Earth history and to understand the processes that occur on and inside the Earth. In typical geological investigations, geologists use primary information related to

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With the advent of space exploration in the twentieth century, geologists have begun to look at other planetary bodies in the same ways that have been

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Relative dating
Methods for relative dating were developed when geology first emerged as a natural science.

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