Dating bedrock planes

In this diagram, subducting slabs are in blue and continental margins and a few plate boundaries are in red.

The blue blob in the cutaway section is the seismically imaged Farallon Plate, which is subducting beneath North America.

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Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction — because the oceanic lithosphere is actually the rigid upper thermal boundary layer of the convecting mantle.

This coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics.

It also provides tools to determine the relative and absolute ages of rocks found in a given location, and also to describe the histories of those rocks.

By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, and also to demonstrate the age of the Earth.

Each mineral has distinct physical properties, and there are many tests to determine each of them.

The specimens can be tested for: In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, solid, upper mantle, which is called the asthenosphere.

All three types may melt again, and when this happens, new magma is formed, from which an igneous rock may once more crystallize.

To study all three types of rock, geologists evaluate the minerals of which they are composed.

This theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.

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