TECTONIC PLATES

CONTINENTAL DRIFT THEORY

• Alfred Wegner, a German meteorologist in 1912, introduced his theory of continental drift.
• He claimed to have noticed that the present day continents looked strikingly similar to a jigsaw puzzle.
• He then proposed this theory: there was a supercontinent called Pangea, which spilt into two other continents, Laurasia and Gondwana.

CONTINENTAL DRIFT THEORY: CONT

• Over millions of years, these continents, floating on the magma beneath the crust, drifted away from each other.
• His most prominent set of evidence was the fact that similar fossils and rocks were discovered on separate continents thousands of kilometers apart.

WHAT ARE TECTONIC PLATES?

• Tectonic plates are slabs of rock that lie on the upper mantle, where there is partially molten rock.
• There is always movement under the Earth’s plates — this movement is called convection currents. Due to these currents and this movement, the continents are graudally drifting away from one another at the approximate rate of 2.5 centimetres a year.
• The Earth is divided into approximately 30 plates.
• There are two types of tectonic plates: continental and oceanic.

WHY DO THE PLATES MOVE?

• The plates of the Earth move because the severe heat within the mantle causes the partially molten rock to swell and rise towards the surface.
• When it spreads out, it cools and falls back towards the centre due to gravity’s pull.
• This cycle continues, and form a current known as the convection current; which is a circular movement that appears when warmer, less dense particles rise, and cooler, denser fluid particles sinks.
• This movement is the cause for plates’ continuous movement.

TYPES OF CRUSTS

• Oceanic: these plates lie beneath the oceans and seas. Their average thickness is about 10 kilometers.
• It is approximately 70-100 million years old and is much more active and thinner in comparison to the continental crust.
• It covers 60% of Earth’s surface, which is made up of basalt rock. This contains elements of silicon, oxygen and magnesium.

TYPES OF CRUSTS: CONT

• Continental: the average thickness for this crust is roughly 20-80 kilometres thick. It is about 3 billlion years old.
• This solid crust is where human beings live and it is less dense than the oceanic crust, despite its superior thickness.
• This crust covers the remaining 40% of the Earth’s surface, which is comprised of granite rock that is rich in silicon, aluminium and oxygen.

TYPES OF PLATE MOVEMENT

• Plate divergence movement: this is the movement where two oceanic plates glide away from each other.
• This results with the formation of new oceanic crusts and mid-ocean ridges.

TYPES OF PLATE MOVEMEMT: CONT

• Lateral slipping plate movement: when two plates slip and slide against each other, there is a colossal amount of friction in the motion — this makes the movement jerky.
• When the pressure from this action is abruptly released, the plates are ripped apart and in the aftermath, an earthquake is present.

TYPES OF PLATE MOVEMENT: CONT

• Convergence plate movement: when plates collide, fragments of the Earth’s crust is destroyed in the process due to the intense force.
• Oceanic and continental convergence: when a thin and dense oceanic plate smashes into a thicker continental plate, it is shoved underneath. This action is called subduction.

TYPES OF PLATE MOVEMENT: CONT

• CONVERGENCE PLATE MOVEMENT CONTINUED
• Two oceanic plate convergence: as two oceanic plates collide, one may be forced beneath the other and magma from the mantle rises. This forms a volcano.
• Two continental plate convergence: since continental plates are thick and gargantuan slabs of rock, it is too light to be pulled into the mantle. Instead, it crunches and folds so that it rises and so, mountain ranges form.

BIBLIOGRAPHY

• http://www.learner.org/interactives/dynamicearth/convergentboundaries/
• http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continent...
• http://oceanexplorer.noaa.gov/facts/plate-boundaries.html
• http://www.learner.org/interactives/dynamicearth/tectonicsmap/
• JacPlus textbook