Plate Tectonic Theory
Alfred Wegener is known as father of plate tectonics, he published this theory in his 1915
book, “On the Origin of Continents and Oceans”. In it he also proposed the existence of the
supercontinent, and named it (Pangaea means "all the land" in Greek). The concept of
plate tectonics was fully accepted in the 1960s. According to the theory, Earth has a rigid
outer layer, known as the lithosphere, which is typically about 100 km thick and overlies a
plastic layer called the asthenosphere. The lithosphere is broken up into about a dozen large
plates and several small ones. These plates move relative to each other. And this movement is
driven by convection currents within the mantle. Convection currents are formed by hot
magma near the core rising towards the surface, while cooler magma near the crust sinks,
setting up a current that causes the plates to move typically at rates of 5 to 10 cm per year.
These plates interact along their boundaries, where they converge, diverge, or slip past one
another. Such interactions are thought to be responsible for most of Earth’s seismic and
volcanic activity. Plate motions cause mountains to rise where plates push together, or
converge, and continents to fracture and oceans to form where plates pull apart, or diverge.
The continents are embedded in the plates and drift passively with them, which over millions
of years results in significant changes in Earth’s geography.
1
, Plate Boundaries
At the locations where two tectonic plates interact, a boundary between the plates exists.
There are three types of plate boundaries viz Divergent boundaries, Convergent boundaries
and Transform boundaries.
Divergent boundaries: A divergent boundary is a fault where the two plates are moving
away from each other. Now, as plates pull apart, several things may occur. First of all,
volcanic activity is common in these areas since mantle easily moves to the surface through
the thin, fractured rock as it separates. Volcanoes are a sign of a divergent boundary. This
happens all along the mid-ocean ridge where magma is constantly streaming to the surface,
creating new ocean floor as the plates separate. As new rock is being created at these
boundaries they are also known as constructive plate margins’. At divergent boundaries,
new crust is being made, but the earth is not getting larger. Why not? Well, at the opposite
ends, crust is being pushed into the earth's interior by colliding plates and being re-melted at
the same rate new crust is formed.
If a continent happens to be a place where a divergent boundary occurs, then the continent
will begin to be torn apart as the sides of the plates separate, creating a rift valley. The
African Rift Valley in East Africa is an example of this occurrence. Eventually, the ocean
will separate East Africa from the rest, making a large island.
In short:
Divergent boundaries – where two plates are moving apart.
The space created can also fill with new crustal material sourced from molten magma that
forms below. Divergent boundaries can form within continents but will eventually open up
and become ocean basins.
i. On land
Divergent boundaries within continents initially produce rifts, which produce rift valleys.
ii. Under the sea
The most active divergent plate boundaries are between oceanic plates and are often called
mid-oceanic ridges.
(1) Mid-oceanic ridges: A mid-ocean ridge or mid-oceanic ridge is an underwater mountain
range, formed by solidification of magma at the divergent plate boundary. Uplifting of
the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust
and create magma where two tectonic plates move away from each other (a divergent
boundary). Example: The mid-ocean ridges of the world are connected and form a single
global mid-ocean ridge system that is the part of the ocean and is nearly 65000km long.
2
Alfred Wegener is known as father of plate tectonics, he published this theory in his 1915
book, “On the Origin of Continents and Oceans”. In it he also proposed the existence of the
supercontinent, and named it (Pangaea means "all the land" in Greek). The concept of
plate tectonics was fully accepted in the 1960s. According to the theory, Earth has a rigid
outer layer, known as the lithosphere, which is typically about 100 km thick and overlies a
plastic layer called the asthenosphere. The lithosphere is broken up into about a dozen large
plates and several small ones. These plates move relative to each other. And this movement is
driven by convection currents within the mantle. Convection currents are formed by hot
magma near the core rising towards the surface, while cooler magma near the crust sinks,
setting up a current that causes the plates to move typically at rates of 5 to 10 cm per year.
These plates interact along their boundaries, where they converge, diverge, or slip past one
another. Such interactions are thought to be responsible for most of Earth’s seismic and
volcanic activity. Plate motions cause mountains to rise where plates push together, or
converge, and continents to fracture and oceans to form where plates pull apart, or diverge.
The continents are embedded in the plates and drift passively with them, which over millions
of years results in significant changes in Earth’s geography.
1
, Plate Boundaries
At the locations where two tectonic plates interact, a boundary between the plates exists.
There are three types of plate boundaries viz Divergent boundaries, Convergent boundaries
and Transform boundaries.
Divergent boundaries: A divergent boundary is a fault where the two plates are moving
away from each other. Now, as plates pull apart, several things may occur. First of all,
volcanic activity is common in these areas since mantle easily moves to the surface through
the thin, fractured rock as it separates. Volcanoes are a sign of a divergent boundary. This
happens all along the mid-ocean ridge where magma is constantly streaming to the surface,
creating new ocean floor as the plates separate. As new rock is being created at these
boundaries they are also known as constructive plate margins’. At divergent boundaries,
new crust is being made, but the earth is not getting larger. Why not? Well, at the opposite
ends, crust is being pushed into the earth's interior by colliding plates and being re-melted at
the same rate new crust is formed.
If a continent happens to be a place where a divergent boundary occurs, then the continent
will begin to be torn apart as the sides of the plates separate, creating a rift valley. The
African Rift Valley in East Africa is an example of this occurrence. Eventually, the ocean
will separate East Africa from the rest, making a large island.
In short:
Divergent boundaries – where two plates are moving apart.
The space created can also fill with new crustal material sourced from molten magma that
forms below. Divergent boundaries can form within continents but will eventually open up
and become ocean basins.
i. On land
Divergent boundaries within continents initially produce rifts, which produce rift valleys.
ii. Under the sea
The most active divergent plate boundaries are between oceanic plates and are often called
mid-oceanic ridges.
(1) Mid-oceanic ridges: A mid-ocean ridge or mid-oceanic ridge is an underwater mountain
range, formed by solidification of magma at the divergent plate boundary. Uplifting of
the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust
and create magma where two tectonic plates move away from each other (a divergent
boundary). Example: The mid-ocean ridges of the world are connected and form a single
global mid-ocean ridge system that is the part of the ocean and is nearly 65000km long.
2
