The Geologic Time Scal1

The Geologic Time Scal1 - The Geologic Time Scale...

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The Geologic Time Scale Radiometric age assignments based on the rates of decay of radioactive isotopes , not discovered until the late 19th century, suggest the earth is over 4.5 billion years old. The Earth is thought older than 4.5 billion years, with the oldest known rocks being 3.96 billion years old. Geologic time divides into eons, eroas, and smaller units. The modern geologic time scale is a hybrid with a relative sequence of units measured against a framework of radiometric (absolute) dates. The time scale was first assembled using fossils and relative dating techniques decades before the development of radiometric dating techniques. The longest duration units of the time scale are the eons . Each eon is subdivided into eras , which are in turn split into periods. Geologists use even smaller time units known as epochs, most commonly in the more recent parts of geologic time. Most geologists recognize three eons: the Archean, the Proterozoic, and the Phanerozoic. The Archean Eon encompasses the time from the formation of the earth until 2.5
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The Geologic Time Scal1 - The Geologic Time Scale...

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