C1.7 Earth and Atmosphere

The Structure of the Earth

The earth consists of a core, mantle and crust, and is surrounded by the atmosphere. 

The thickness of the crust can vary from 5km under the oceans to 70km under the continents.

The thickness of the mantle is 3000km and it behaves like a solid, but it can flow in parts very slowly.

The core is about half the radius of the earth. It's a mixture of nickel and iron. This is the inner core.

Tectonic Plates

The Earth's crust is broken up into section called tectonic plates. The tectonic plates are continuously moving very slowly (a few cm every year). 

The tectonic plates are moved by convection currents in the mantle. Heat from natural radioactive processes in the core causes parts of the mantle to become less dense and float to up towards the crusts. The mantle cools, becomes more dense and sinks back down. This constant movement of the mantle causes the tectonic plates to move.

The movements in the Earth's crust can be sudden, disastrous and not readily predictable.

• Earthquakes and / or volcanic eruptions occur at the boundaries between tectonic plates.

• Changes that occur at plate boundaries causes earthquakes and volcanic eruptions.

Wegener's Theory and Continental Drift

Alfred Wegener proposed his theory of continental drift. He suggested that all the continents used to be joined together as a agiant land mass called Pangea. In the time between 250 million years ago and today the continents moved apart to form the world as we know it now. Wegener was suggesting the continents were slowly moving apart from eachother.

Wegener's theory was not accepted for a long time because:

• he could not explain how the continents were moving
• lack of evidence
• he was a meteorologist not a geologist

Evidence of Pangea - Africa and South Africa

• Coastlines had the same shape
• Some rock pattern of layers of sedimentry rock
• Same types of fossils found on two coastlines but no where else and snimals couldn't swim
  • Can be explained by the previous theory of a 'land bridge' from Africa to South America suggested by Edward Suess

Seafloor spreading

The Earth's crust and top of the mantle are broken up…