What is the Earth's structure like?

The Earth's Structure

The earth is made up of the following parts:

Crust - the solid outer layer of the earth on which we walk.
Mantle - the next layer towards the centre of the earth. This is the thickest layer and is made of semi-molten rock called magma.
Outer core - the nest layer towards the centre of the earth. This is made of liquid rock.
Inner core - the centre of the earth. This is made of solid rock and is at a temperature of up to 5,500 degrees Celsius.

Tectonic Plates

Tectonic plates are the huge slabs of rock that form the earth's crust and that float on the mantle (the semi-solid rock beneath the crust. There are two types of plates:

Continental plates are thick but light in weight (less dense) and form land. They are made of granite.
Oceanic plates are thinner but heavier (more dense) and have sea over them. The are made of basalt.

The movement of plates is called continental drift. This can push the plates together or push them apart. Continental drift occurs due to the movement of the magma in the mantle below the plates. The movement of magma is caused by convection currents generated by the immense heat at the earth's core. Convection currents are heated plumes of magma which create crustal plate movement.

The Location of Earthquakes and Volcanoes

Earthquakes and volcanoes are primarily found at plate boundaries. The mantle is much hotter than the crust and its rock is molten. At the boundaries between plates, molten magma is able to force its way to the surface and escape as lava.

Plate Boundaries

The edges where the plates meet are called plate boundaries.

There are four types of plate boundary: constructive, destructive, conservative (or sliding) and collision.

Constructive Plate Boundary

Two plates move apart.
Magma rises to the surface, due to gas bubbles in the magma that make it lighter than the surrounding rock.
Volcanoes are formed.
Gentle eruptions occur which may continue for years.

Most constructive boundaries are under the sea and form chains of volcanic islands. The Mid-Atlantic Ridge is the most famous of these chains.

Destructive Plate Boundary

An oceanic and continental plate collide.
The heavier oceanic plate sinks under the continental plate into what is know as a subduction zone.
The melted crust rises (due to the gas bubbles in the magma that make it lighter than the surrounding rock) to form explosive, dangerous volcanoes.
When the two plates rub together, friction occurs, leading to earthquakes.

The most famous destructive boundary is the Pacific Ring of Fire, which forms a band of earthquakes and volcanoes round the edge of the Pacific Ocean. A destructive plate boundary was also the cause of the Soufrière Hills volcano in Montserrat.

Conservative (or sliding) Plate Boundary

Two plate slide past each other.
The plates become locked and tension builds up over years.
Eventually the plates will jolt past each other, causing powerful earthquakes.
Volcanic activity does not occur.

The most famous of these is the San Andreas fault.

Collision Plate Boundary

Two continental plates push together.
Neither sinks beneath the other as they are both made from light rock.
The plates buckle to form fold mountains and violent earthquakes occur.
Volcanic activity does not occur.
The area where the earthquake starts underground is known as the focus. Directly above the focus, on the Earth's surface, is the epicentre.

The Himalayas are the most famous fold mountains.

This map shows the location of the four different plate boundaries.

Google Sites

Report abuse