Absolute geologic age dating

26-Jul-2016 22:26

The age of a rock in years is called its absolute age.

Geologists find absolute ages by measuring the amount of certain radioactive elements in the rock.

In fact, sedimentary rocks are, in a sense, trash from the Earth's surface deposited in basins.

Because the Earth's crust is continually changing, i.e due to uplift, subsidence, and deformation, erosion is acting in some places and deposition of sediment is occurring in other places.

The absolute ages of rocks taken from the different time periods have shown that the time periods were of greatly differing lengths.

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By carefully digging, we have found that each trash pit shows a sequence of layers.One way is to look at any fossils the rock may contain. When you find layers of rocks in a cliff or hillside, younger rocks are on top of older rocks.If any of the fossils are unique to one of the geologic time periods, then the rock was formed during that particular time period. But these two methods only give the relative age of rocks--which are younger and which are older. Or how do we know how long ago a particular group of fossilized creatures lived?Thus, in a sequence of layers that have not been overturned by a later deformational event, the oldest layers will be on the bottom.This is the same principle used to determine relative age in the trash pits discussed previously.

By carefully digging, we have found that each trash pit shows a sequence of layers.One way is to look at any fossils the rock may contain. When you find layers of rocks in a cliff or hillside, younger rocks are on top of older rocks.If any of the fossils are unique to one of the geologic time periods, then the rock was formed during that particular time period. But these two methods only give the relative age of rocks--which are younger and which are older. Or how do we know how long ago a particular group of fossilized creatures lived?Thus, in a sequence of layers that have not been overturned by a later deformational event, the oldest layers will be on the bottom.This is the same principle used to determine relative age in the trash pits discussed previously.As shown in the diagram above, uranium is trapped in a newly formed rock.