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Geologists study rocks and fossils, or remains of living things that have been preserved in the ground. The rocks and fossils tell the story of Earth from when its crust formed billions of years ago to the present. Geologists have mapped out a time scale that is a “calendar” of Earth’s geologic history.
It is important to study this because it allows scientist to reconstruct the surface and surface conditions of the ancient earth. This in change, allows us to know how Earth has changed over the years.
The Geologic Time Scale
Geologists divide geologic time into a series of eons. Each eon is in turn divided into smaller and smaller units of time. The two oldest eons are part of what is called Precambrian time. The third eon is called the Phanerozoic.
The Geologic Record
The surface of Earth consists of layers of rock formed from pebbles, sand, and mud deposited by water, wind, or glaciers. The oldest layers are lower down and the more recent layers piled up on top.
Radiometric Age Dating
Radiometric dating calculates an age in years for geologic materials by measuring the presence of a short-life radioactive element (carbon isotopes) or a long-life radioactive element plus its decay product
Geologists use these dates to further define the boundaries of the geologic periods shown on the geologic time scale.
Relative and Absolute dating
In relative dating, we determine which things are older or younger based on their relationships.
Absolute dating methods measure the physical properties of an object itself and use these measurements to calculate its age.
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