When tectonic plates move, what can happen
- earthquakes at the plate boundaries
- volcanoes at the plate boundaries
- over millions of years, countries and continents can move apart (evidence suggests that South America and Africa were joined at one point, but through tectonic plate movement they have moved apart)
What is the outer layer of the earth called, and what is it made of
Lithosphere
- relatively cold, brittle and rigid
- made of the crust and part of the mantle that lies directly underneath
Why is the theory of plate tectonics now widely accepted
- it explains the evidence
- it has been tested, and the results discussed by many scientists
How is energy from the earths core transferred to the surface
Through convection currents in the mantle. These convection currents move the plates
What are the 2 types of plates, and what are their densities
- oceanic plate; denser than continental ones
- continental plates; float higher than the mantle
What is subduction
The edges of an oceanic edge are denser than the centre; so when an oceanic plate collides with a continental plate, the oceanic plate sinks below the continental plate. As it sinks, it pulls more of the oceanic plate down with it.
How are earthquakes and volcanoes made from subduction
Earthquake-as the sinking plate descends it may get stuck and the suddenly move
Volcano-further down, it partially melts and some of the magma works its way up the surface and creates a chain of volcanoes along the edge of the plate
When magma cools it becomes…
Igneous rock
How can you tell how igneous rock has cooled
By looking at its crystals:
- rapid cooling (close to the surface) has SMALL crystals
- slow cooling (further from the surface and better insulated) has LARGE crystals
Why do volcanoes erupt in different ways
Different compositions of magma produce different types of lava, which causes different types of eruption.
What is the continental drift theory
In 1914, Alfred Wegener suggested that the continents were formed from one ‘supercontinent’ that was splitting apart at the time of the dinosaurs
What is the main structure of the earth
Inside to out:
- iron core
- mantle
- rocky crust
- tectonic plates
