# Plate Tectonics

## Plate boundaries

There are 4 types of plate boundaries. Convergent, Convergent with subduction, divergent, and transform. Convergent occurs when two plates collide together. Convergent with subduction occurs when two plates collide and the thinner and less dense plate is forced down into the mantle. Divergent occurs when two plates move away from each other. Transform occurs when two plates slide past each other.

## What do plate boundaries form

Divergent (on land) form rift valleys and volcanoes. Divergent (in ocean) form volcanoes and sea floor spreading. Convergent form mountains. Convergent (subduction) form trenches, volcanoes, and mountains.

## The theory of plate tectonics

The theory of plate tectonics is the theory that the outer rigid layer of the earth (the lithosphere) is divided into a couple dozen plates that move around across the earth's surface.

## The 3 layers of the Earth and their importance

The 3 layers of the earth are the crust, mantle, and the outer and inner core. The crust is where all life lives. The mantle is mostly molten rock and where many of our precious metals start. The core is the densest part of the Earth mostly composed of iron, the rotation of the core is what gives the Earth its magnetic field that protects us from cosmic radiation called the Magnetosphere.

## Continental drift

Continental drift is the hypothesis that todays continents were once part of a single landmass. This hypothesis was created by Alfred Wegener.

## Evidence for continental drift

Alfred Wegener's evidence was that the continents fit together, glacial till deposits, and the apparent shifting of climatic belts over time.

Sea floor spreading occurs when a new sea floor rock forms and it pushes the existing rock in the opposite direction away from the ridge. This was discovered by Harry Hess.

## How does sea floor spreading help to explain continental drift

When plates move apart due to sea floor spreading it carries the continents with it, so the contents are moving away from each other due to sea floor spreading.

## How does convection help with plate movement

When large convection currents transfer heat to the surface, where less dense magma breaks apart the plates at the spreading points creating plate boundaries.

## Ring of Fire

The Ring of Fire is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. It is a 40,000 km horseshoe shape that's consists of oceanic trenches, volcanic belts, and plate movements.