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The lithosphere is the outermost layer of the Earth and other solid planets, consisting of the upper crust and upper mantle. It is made up of tectonic plates that slowly drift and can create massive structures over millions of years. The lithospheric activity can have a profound effect on the surface above it, such as decreasing the global temperature. Geoscientists study the properties of the deep lithosphere by examining special rocks uplifted through deep volcanic tubes.
The lithosphere, Greek for “rocky sphere”, is the outermost shell of the Earth. The term is also used to refer to the outermost rocky shell of other solid planets. It is a relatively thin layer, 31 to 62 miles (50 to 100 km) thick under the oceans and 93 miles (150 km) thick on the continents. This layer is composed of the upper crust, about 3 miles (5 km) thick in the oceans and 40.3 miles (65 km) in the continents, and the upper mantle, which makes up the remainder. Separating the crust and upper mantle is the Mohorovičić discontinuity, the point at which rocks become plastic rather than solid. Below the lithosphere is the asthenosphere, which continues the upper mantle, and is approximately where the mantle becomes liquid.
This planetary shell is made up of lithospheric plates, otherwise known as tectonic plates, that drift slowly over time periods of millions of years. Their drift rate is comparable to the rate at which a person’s fingernails grow. However, over long periods of time, they can create massive structures, such as the Himalayan Mountains in Tibet. mt. Everest and the other mountains were formed when the tectonic plate under India made its way into Asia.
Using accurate measurement methods and the study of strata, paleontologists have determined that tectonic plates have been shifting across the planet’s surface since at least 600 million years ago, when various fossils appeared. During this time, the continents started out as separate, then merged together into the giant continent Pangea, only to split after a few hundred million years and create the continents people are familiar with today.
Lithospheric activity can have a profound effect on the surface above it. When Australia finally separated from Antarctica 50 million years ago, it allowed a new ocean current, the Circumpolar Current, to flow around Antarctica and reinforce its own cooling. This froze the continent, which was previously forested, killing all but the hardest of life. It has also decreased the average global temperature by several degrees.
Although humans cannot delve very deep into the earth’s crust with current technology, geoscientists can study the properties of the deep lithosphere by examining special rocks, or xenoliths, uplifted through deep volcanic tubes.
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