Plate Tectonics Explained

The interior structure of Earth is chemically divided into an outer solid crust, the mantle, a liquid outer core, and a solid inner core. The core is largely composed of iron, along with nickel and silicon. Other lighter elements are usually in the crust.

The core is divided into two parts, the solid inner core and the liquid outer core. The inner core is thought to be solid and primarily made up of iron and some nickel. The outer core is all around the inner core and is believed to be made up of liquid iron mixed with liquid nickel. The outer core is about 2890 to 5100km. The inner core is 5100 to 6378km.

Earths mantle is mainly composed of substances high in iron and magnesium. The melting point of every substance depends on the pressure and the deeper we go the higher the pressure becomes. Because of this the upper mantle is said to be semi-molten and the lower mantle solid. The upper mantle iron-substances are semi-molten because it is hot and they are under little pressure, lower mantles iron-substances are solid because they are under a lot of pressure. The mantle is 35 to 2890km.

Earths crust ranges from 5 to 70 km in depth. The thinnest parts are the oceanic crust made of dense iron magnesium silicate rocks and underlie the ocean basins. The thicker crust is continental crust, composed of sodium potassium aluminum silicate rocks. The crust varies from 0 to 35 km or 5 to 70km.

Convection currents occur because the density of a fluid is related to its temperature. Hot rocks lower in the mantle are less dense than the cooler rocks above. The hot rocks rise and the cooler rocks sink because of gravity. Convection currents are thought to be the driving mechanism of plate movement. Convection currents cause convergent and divergent movements. When the rising part of the convection current rises it causes the upper mantle to move upward and in a lateral direction. This causes the mantle to split and new material to rise creating new ocean crust. The downward motion of the convection current pulls the mantle crust downward at convergent boundaries. When part of the mantle crust is uplifted the weight of the lifted part, pushes the sinking mantle down, causing motion in the tectonic plates.

A convergent boundary is where two tectonic plates move towards each other. And when they collide they form either a subduction zone with its associated island arc or an orogenic belt and associated mountain range. When the two plates collide, one of the plates is pushed underneath the other. This then forms oceanic trenches in which the Earth's crust is pushed under into the mantle where it becomes molten. The oceanic trenches are several hundred kilometers long but narrow. They also are the deepest parts of the ocean floor. These boundary types also produce mountains. Mountains are made when convergent boundaries collide but instead of one going under they both are pushed up by the others force. For this to happen neither of the boundaries can be more or less dense than the other. There are three types of convergent boundaries: oceanic plate-continental plate convergence, oceanic plate-oceanic plate convergence, and continental-continental plate convergence. An example of this type of boundary is the collision between the Eurasian Plate and the Indo-Australian Plate which is forming the Himalayas.

A divergent boundary is where the plates are moving away from each other. These areas can form in the middle of continents but eventually form ocean basins. Divergent boundaries make ocean ridges like the Mid- Atlantic ridge. At divergent boundaries the floor is higher than anything else around it. This is because where the plates are moving away from each other there is a crack where new magma constantly flows upward toward the surface through a gap called a rift onto the ocean floor making the surrounding area move outward. Sometimes submarine volcanoes might also be formed. Continental crust is often split along divergent plate boundaries. An oceanic ridge is an underwater mountain range, usually formed by plate tectonics.

Abyssal plains are flat or very gently sloping areas of the ocean basin floor where rocks slowly sink into the ground because they have no heat energy supporting them below. They result from the layering of an uneven surface of the ocean floor with fine-grained sediments like clay and silt deposited from turbidity currents. They usually form in between the foot of a continental rise and a mid-oceanic ridge.

A transform boundary happens when tectonic plates slide and grind against each other along a transform fault. As the plates slide past each other the grinding and scraping start forming cracks and faults. An example of this is the San Andres fault in California. Most transform boundaries are found on the ocean floor, where they often offset active spreading ridges to form a zigzag plate boundary. A few transform boundaries