Plate Tectonics Continental Drift

The Earth’s crust (lithosphere) is made up of plates that float on a flexible/plastic layer of hot magma. These plates are not fixed. In fact, although the continents seem stable, they are always moving. The way they move is predictable. Their movements guide the way our earth is formed. Plate Tectonics

Crustal Plate Boundaries

Plate Boundaries

Long ago the continents were in completely different places. Over the billions of years the Earth‘s changes have moved the continents in and out of their current locations. This is called continental drift. It is governed by the massive heat energy coming from the center of the Earth. Continental Drift

Pangaea

Laurasia and Gondwanaland

Continental Drift

Plate Types There are two kinds of plates: Continental plates are the plates that are made up of land masses. These are simply the big masses of rock that form the continents. These plates are lighter. They “float” higher. Oceanic plates are the plates that sit under the oceans. They are the big masses of rock that like a bowl, hold the oceans. These plates are denser. They “sink” lower. Plate Types

The oceans and continents all sit on different tectonic plates The oceans and continents all sit on different tectonic plates. Like all territories, these plates have edges that we call boundaries. How the edges, or boundaries, behave determines what we call them. There are three kinds of plate boundaries: Convergent Divergent Transform Plate Boundaries

Plate Boundaries

Convergent Boundaries To converge means to come together. A convergent plate boundary is where two plates meet and smash up against one another. Sometimes this makes mountains as when two continental plates come together. Sometimes this makes volcanoes, as when a continental and an oceanic plate come together. When this happens, one plate goes under the other. We call that a subduction zone. Convergent Boundaries

Mountain Making Convergence

Subduction Zone

Subduction Zone

Oceanic Convergence

Ring of Fire Subduction Zones are where volcanoes appear There is a huge area of the Earth where most subducting activity is created. There are volcanoes all around it. For this reason we call it the Ring of Fire. Ring of Fire

Ring of Fire

Divergent Boundaries To diverge means to separate. A divergent plate boundary is where two plates are pulling apart from one another. There are two kinds: One kind is an oceanic spreading ridge. There is one going down the whole of the Atlantic ocean. Where it spreads apart new crust is formed where the magma comes up from the earth and cools. It is made of two oceanic plates spreading apart. The other kind is a rift zone. This is where the continental plates are tearing apart. It is made of two continental plates spreading apart. Divergent Boundaries

Divergent Boundaries

Mid Atlantic Ridge

Mid Atlantic Ridge

Rift Zone

Iceland Rift

Iceland Rift

Iceland Rift

Hawaii Rift

A transform boundary is where two plates are sliding past one another. They are on continental and oceanic plates. They make a lot of earthquakes. We have a HUGE one – the San Andreas Fault. It is the cause of most of our earthquakes in California. Transform Boundaries

Transform Fault

Oceanic Transform Fault

San Andreas Fault

Transform Boundary Damage

Transform Boundary Damage