Theory of Plate Tectonics

Science, Grade 6


Table Of Contents: Theory of Plate Tectonics

1. What Is the Theory of Plate Tectonics?
The theory of plate tectonics was proposed in the 1960s. It states that the lithosphere is broken into pieces called tectonic plates that are moving on top of the upper mantle. The plates carry both the continents and the ocean floors.
2. Tectonic Plates in Motion
According to the theory, the tectonic plates are in motion due to the movement of convection currents in the mantle.
3. Tectonic Plate Boundaries
The tectonic plates move against each other at their boundaries, resulting in intense geologic activity, such as volcanoes, earthquakes and mountain formation. There are three types of plate boundaries—divergent, convergent and transform.
4. Divergent Plate Boundaries
New crust is created at divergent boundaries, where two plates are moving apart. This type of boundary creates mid-ocean ridges in the oceanic crust and rift valleys on land.
5. Convergent Plate Boundaries
Convergent boundaries, where two plates are moving together, can occur between an oceanic and continental plate, two oceanic plates or two continental plates.
6. Subduction Zone
A subduction zone occurs when a dense oceanic plate is pushed down into the mantle below another plate. Over time, the subducted crust melts in the mantle. This geologic activity creates volcanic islands in the oceans and volcanic arcs on land.
7. Mountain Range Formation
Subduction does not occur at the convergent boundary of two continental plates. Instead, the crust is pushed upward and mountain ranges are formed.
8. Transform Boundary
A transform boundary occurs when plates slide past each other, such as the San Andreas fault in California. These boundaries are called conservative because plate material is neither created nor destroyed.