Dating earth radioactivity

The study of strata is called stratigraphy, and using a few basic principles, it is possible to work out the relative ages of rocks.

Just as when they were deposited, the strata are mostly horizontal (principle of original horizontality).

Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).

dating earth radioactivity-57

" First, the relative age of a fossil can be determined.

Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event.

The principle states that any geologic features that cut across strata must have formed after the rocks they cut through (Figures 2 and 3).

According to the principle of original horizontality, these strata must have been deposited horizontally and then titled vertically after they were deposited.

For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.

By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.

Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).

The principle of superposition builds on the principle of original horizontality.

Third, magnetism in rocks can be used to estimate the age of a fossil site.

This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks.

The principle of superposition states that in an undeformed sequence of sedimentary rocks, each layer of rock is older than the one above it and younger than the one below it (Figures 1 and 2).

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