Earth's surface is made up of a set of tectonic plates. The plates come together at plate boundaries.

Tectonic plates move across Earth's surface, interacting in three ways. This results in three different types of plate boundaries. Plates can move toward each other, creating a convergent boundary. Plates can move apart, creating a divergent boundary. Plates can also slide past each other, creating a transform boundary.

Earth's major and minor plates. Earth's surface is made up 12 major plates and several minor plates.

Divergent plate boundaries occur where two plates are spreading apart.

Divergent plate boundaries are also sometimes called spreading ridges because seafloor spreading takes place there. Most divergent plate boundaries are located in the middle of oceans.

The spreading center in the middle of the Atlantic Ocean is called the Mid-Atlantic Ridge. At this divergent plate boundary, the North American plate and the Euruasian Plate are moving apart.

At divergent plate boundaries, new ocean crust forms as the plates move away from each other. So oceans with divergent plate boundaries are getting bigger. This is why the Atlantic Ocean is growing larger.

When divergent plate boundaries are found on land they split the continent apart. First the continental crust thins and forms a rift valley. If the plates continue to diverge, a midocean ridge develops and new seafloor is created. The East African Rift is currently splitting the eastern part of Africa away from the main African continent. Eventually a new sea will grow between the two landmasses.

Divergent plate boundaries. New ocean crust and earthquakes are found where two plates move apart.

Plates move toward each other at convergent plate boundaries. When two plates move toward each other, there are three possible results depending on the type of crust that is colliding.

Two oceanic plates converge to create a subduction zone. When two oceanic plates collide, the denser of the two plates plunges beneath the other. This process is called subduction and occurs at a deep-ocean trench. When the sinking plate gets deep enough into the mantle, it gets hot enough to partially melts. Above this partial melt zone is a chain of volcanoes. The volcanoes are on the plate that overlies the subduction zone. These volcanoes create oceanic islands and together are called an island arc; Japan is an example.

In the western Pacific, the Pacific plate (an oceanic plate) is subducting beneath the Philippine Plate (another oceanic plate). This subduction zone creates the Marianas Trench, the deepest spot on Earth. The Marianas Islands are a chain of volcanoes that form on the Philippine plate.

Convergent plate boundary: ocean-ocean. When two oceanic plates converge, one plunges beneath the other at a trench. This region is called a subduction zone.

A continental and oceanic plate converge to create a subduction zone. There is also a deep-sea trench and a line of volcanoes.

An oceanic plate is always denser than a continental plate so the oceanic plate subducts beneath the continental plate. Subduction takes place at a deep sea trench. Partial melting of the subducting plate may form a chain of volcanoes called a volcanic arc on the continental crust above. The Cascades volcanoes of the Pacific Northwest are an example.

Along the western side of South America, the Nazca plate (an oceanic plate) is subducting beneath the South American plate. A trench called the Peru-Chile Trench has formed where the two plates meet. The Andes Mountains have formed along the edge of South America.

As a result of this subduction, and other subduction around the Pacific, the Pacific basin is getting smaller.

Convergent plate boundary: ocean-continent. Where an oceanic plate collides with a continental plate, the oceanic plate subducts at the deep sea trench and creates a volcanic arc.

Two continental plates converge to create a mountain range. Continental plates are too buoyant to be pushed into the mantle. Two converging continental plates push upward and form a mountain range.

The Himalayan Mountains in Asia are the result of a collision at a convergent plate boundary. Here the Indian plate is colliding into the Eurasian plate at the rate of about 5 centimeters a year. As the continental crust pushes upward, the Himalayan Mountains continue to grow taller.

Convergent plate boundary: continent-continent. Mountain ranges form in these types of boundaries.

Plates move past each other at transform plate boundaries. These plates can both be oceanic or continental.

Where continental plates move past each other, the motion isn't smooth. The plates move along faults, or cracks in the crust. Plates move in big jolts known as earthquakes, which are very common along transform plate boundaries.

The San Andreas Fault in California is probably the best known transform plate boundary. Here the North American plate and the Pacific plate slide past each other at about 5 centimeters each year. Along a small portion of the fault, there are frequent earthquakes and so none is too big. Along most of the fault, though, earthquakes are infrequent and can be extremely large and damaging.

The San Andreas Fault runs from the Gulf of California northwest to Mendocino County in northern California.

Transform plate boundaries. The San Andreas Fault is just one example of a transform plate boundary. The continental crust on the west side of the fault is moving northwestward relative to the crust on the east side of the fault.

The Breakup of Pangaea. The supercontinent of Pangaea broke up and formed the continents we see today.

Divergent plate boundaries broke Pangaea apart and created oceanic crust between the continents. The continents continue to move apart as the Atlantic Ocean grows.

Fun fact: Plate speed - Estimates of the speed of plate movements vary. Generally speaking, scientists agree that plates move between 1 - 10 cm in a year. This is calculated based on the apparent locations of the continents in the past combined with more modern satellite technology today.

Pangaea first broke apart into two supercontinents, Laurasia in the north and Gondwanaland in the south. The continents continued to separate into their current configuration.