First 447 words of the document:
The structure of the earth:
The Crust the outermost layer of the earth is the coolest and thinnest.
The Mantle this section has the properties of a solid but it is a very slow moving liquid rock.
Outer core this is made from iron and nickel. It is so hot that the iron is a liquid.
Inner core this is also made of iron and nickel. It is hotter than the outer core but the iron is solid. This is
due to high pressures.
The earth's crust is crack into huge pieces called tectonic plates.
Deep with in the earth, radioactive decay produces vast amounts of energy and this heats up the molten
minerals in the mantle.
The minerals expand, become less dense and rise towards the surface and are replaced by cooler material.
It is these convection currents that slowly push the tectonic plates over the surface of the Earth.
This idea was first put forward by Alfred Wegener in 1915 but not everyone agreed with him.
Earthquakes and volcanoes:
Where the tectonic plates meet, huge forces are exerted. These make the plates buckle or deform and
mountains may be formed if the two plates have the same density.
Eg: The Himalayas Mountain was produced when the Indian and Eurasian collided.
If a continental plate and an oceanic plate collide, the oceanic plate dips below the continental plate and
rejoins the magma. This happens because the oceanic plate is denser than the continental plate. This is called
a destructive plate margin.
Eg: In South America, the Pacific Ocean bed dips beneath South America.
Earthquakes happen where the tectonic plates meet. They happen when the plates suddenly slip past each
They are difficult to predict when they happen because:
They don't know where it is going to happen
They don't know when it is going to happen
The atmosphere was formed by volcanoes millions and millions of years ago.
When volcanoes erupted they gave off gases such as Carbon Dioxide, Sulphur Dioxide, Nitrogen Dioxide,
At first the planet was very hot
But as it cooled, a number of changes happened...
The water vapour condensed and it started to rain. Weathering of rocks began.
Lightening produced nitrogen and ozone
The surface water was an excellent place for chemical reactions to start happening
Photosynthesising bacteria and later plants began to change CO2 to O2.
Other pages in this set
Here's a taster:
The early atmosphere was made up mainly of Carbon Dioxide with some water vapour and Nitrogen but
hardly any Oxygen.
Scientists look at the atmospheres of other planets like Mars and Venus to study what our atmosphere
might have been like 200 million years ago. They also look at ice cores.
The composition of the modern atmosphere: