Earth and atmosphere, Year 7: more practice

The mantle

提示It is a thick layer of hot rock.

为什么Beneath the crust is the mantle, a thick layer of hot rock that moves very slowly.

The core

提示It is the hottest part of the Earth.

为什么The Earth's core is mostly iron and nickel. The outer part is liquid and the inner part is solid.

It is too deep and too hot

提示Think about what happens to temperature the further down you go.

为什么The deeper you go the hotter it gets. Drills and equipment cannot cope with the temperature and pressure.

The crust

提示Compare it to the skin of an apple.

为什么The crust is only a few kilometres thick under the oceans and a few tens of kilometres thick under the continents.

Ice takes up more space than water, so it expands and forces the crack wider

提示What happens to the volume when liquid turns solid?

为什么This is freeze–thaw weathering. It repeats night after night until pieces of rock break off.

Chemical weathering

提示Is the rock changed by a reaction, a living thing or just a force?

为什么Weak acid in rain reacts with limestone and eats it away. A chemical reaction is involved, so it is chemical weathering.

Biological weathering

提示A living thing is doing the work.

为什么Biological weathering is caused by plants and animals, such as roots growing in cracks.

Physical weathering

提示Is the rock changing into a new substance or just breaking up?

为什么Repeated expanding and contracting stresses the rock until it breaks. No new substance forms.

Argon

提示It is an unreactive noble gas.

为什么Argon makes up a little under 1% of the air. It is a noble gas, so it does not react.

Its gases are not chemically joined and can be in different amounts

提示Think about whether the parts are bonded to each other.

为什么The gases in air are just mixed. The amounts can vary from place to place and the gases keep their own properties.