The Earth and Plates

The Earth

The Earth has a number of different layers

The inner core, the outer core, the mantle, continental crust and oceanic crust.


  1. The inner core – Extremely hot, solid, made of iron and nickel
  2. The outer core – Liquid layer, made of iron and nickel
  3. Mantle – Hot, made of semi-solid rock
  4. Continental and Oceanic Crust – Thinnest layer, Thicker under the continents than under oceans

(*Think of a Ferrero Rocher Chocolate!!!)


Plate Tectonics

The Earth’s surface is divided into different plates

These plates are slowing and constantly moving (1.5cm/year) because of convection currents

Convection currents are movements in the mantle because of the heat from the core

Plates are not fixed. Plates move towards each other, away from each other and past each other.

This helps us to understand how mountains, volcanoes and earthquakes, for example, occur.

Alfred Wagner was the person that observed this theory. He noticed coastlines fit together and also similar fossils were found at different coastlines.

The boarder between 2 tectonic plates is called a boundary

Plates move in different directions

There are 3 types of plate boundaries:

  1. Divergent – two plates that are moving away from each other
  2. Convergent – Two plates pushing towards each other
  3. Transform – two plates sliding past each other

Divergent Boundary:

Sea floor spreading occurs at divergent boundaries.

Plates pull apart and a crack appears

Magma rises up and fills the crack in the ground

This forms a raised ridge called a mid-ocean ridge

The magma spreads outward forming new crust

When two plates diverge, a valley-like rift occurs.

This is a dropped zone where the plates are pulling apart

Convergent Boundary:

At some convergent boundaries, an oceanic plate collides with a continental plate.

Oceanic crust is normally denser and thinner than continental crust.

The denser oceanic crust gets bent and pulled under, or subducted, beneath the lighter and thicker continental crust.

This is called a subduction zone2

As the oceanic crust sinks, a deep oceanic trench, or valley, is formed at the edge of the continent.

The crust continues to be forced deeper into the earth.

High heat and pressure cause trapped water and other gasses to be released from it. This makes the base of the crust melt, forming magma.

This magma rises up into magma chambers and feeds and creates volcanoes

Example: Ring of Fire, Pacific Ocean

When the magma cools is creates new land/islands called island arcs

Example: Mariana Islands, Pacific Ocean

Earthquakes can be caused as a result of plates colliding

Earthquakes can lead to tsunamis because of a sudden shift on the Ocean floor.

When 2 plates collide, the rocks are not subducted with the plate.

They are crunched, scraped and folded at the boundary and then lifted up to form mountains.

This process happens over time

Example: Himalayan Mountains


Transform Boundary

Plate boundaries are not all smooth

As the plates slide passed each other tension builds up.

When this tension/stress is released suddenly, the sudden movement results in an earthquake

These boundaries can be referred to s faults or ‘strike-slip faults’

Example: San Andreas Fault, California

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