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USGS CMG InfoBank: Superposition

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Comment: 09:06 - 09:48 (00:42)
Source: Annenberg/CPB Resources - Earth Revealed - 10. Geologic Time
Keywords: "James Sadd", "geologic age", "Principle of Superposition", superposition

Our transcription: Although arguments about the age of the Earth raged among the intellectual community throughout the Nineteenth Century, most scientists have accepted the premise that the Earth must be millions of years old, instead of just a few thousand.
And although they were not yet able to measure the age of rocks, geologists realized they could determine the sequence of events in Earth's history by combining careful observation with some simple logic.
They first reasoned that any layered sequence of rocks is formed with the oldest layer at the bottom and successively younger layers on top.
This principal called "superposition" allows us to place rock units in a historic sequence according to their relative age.

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