THE LITHOSPHERE

The lithosphere is the outermost solid layer of the Earth, comprising the crust and the upper mantle. It is the layer of the Earth that we live on and is made up of solid rock.

The lithosphere is divided into 6 main tectonic plates, which are in constant motion due to the convection currents in the mantle. The lithosphere is made up of a variety of rock types, including igneous, sedimentary, and metamorphic rocks.

THE CRUST

The crust is the outermost layer of the Earth and is made up of solid rock. It is divided into two types: continental crust and oceanic crust.

Continental crust is the top layer of the Earth's crust. It is made up of granitic and sedimentary rocks and is generally thicker and less dense than oceanic crust. Continental crust ranges in thickness from 35 to 70 kilometers and makes up about 29% of the Earth's crust.

Oceanic crust is the layer of the Earth's crust found under the oceans. It is made up of basaltic rock and is generally thinner and denser than continental crust. Oceanic crust ranges in thickness from 7 to 10 kilometers (4 to 6 miles) and makes up about 71% of the Earth's crust.

Both types of crust are constantly moving due to the convection currents in the mantle, but oceanic crust is more dense and sinks more easily, causing it to be recycled back into the mantle. Continental crust, on the other hand, is less dense and is more likely to be uplifted and transformed into mountains.

PLATE BOUNDARIES

There are four main types of plate boundaries:

1. Constructive (divergent)

2. Destructive (convergent)

3. Collision (convergent)

4. Conservative

Constructive (or divergent) boundaries occur where two plates are moving away from each other. At these boundaries, new crust is generated as magma rises to the surface and solidifies. This is how oceanic crust is formed at mid-ocean ridges. As the plates move apart, magma rises to fill the gap and solidifies to form new oceanic crust. This process can also lead to the formation of rift valleys and underwater mountain ranges.

Destructive (or subduction) boundaries occur where two plates are converging, with one plate being pushed beneath the other. This process is known as subduction and it typically occurs when an oceanic plate meets a continental plate. The denser oceanic plate sinks beneath the continental plate and is recycled back into the Earth's mantle. As the plate descends deeper into the Earth, it can cause earthquakes, volcanoes, and mountain building.

Collision boundaries also occur when two plates converge, but in this case, both plates are typically continental plates. They push against each other and can cause the formation of large mountain ranges, like the Himalayas.

Conservative boundaries occur where two plates are sliding past each other horizontally. This process is known as strike-slip faulting, and it can cause earthquakes. Transform boundaries, such as the San Andreas Fault in California, are examples of conservative plate boundaries. These boundaries are also referred to as "conservative" because the plates themselves are not destroyed, but instead move along the boundary.

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