Soil is the uppermost layer of the Earth. It is a mixture of different things.
Soil contains gases such as carbon dioxide, oxygen, nitrogen, methane and radon.
Air and water fill the gaps between particles of soil.
The minerals in soil come from finely broken down rock.
Organic matter includes both living and decaying animals and plants.
Layers of soil
There are four main processes involved in soil formation:
Rainfall adds water.
Dust adds minerals.
Animal waste adds organic matter and nutrients.
Decaying plants and animals add organic matter.
Humans add fertiliser. Fertilisers contain minerals and nutrients. Natural fertilisers are made from animal waste and organic matter. Man-made fertilisers are made from chemicals.
Water evaporates (turns into gas when hot) into the air.
Soil particles can wash away in storms.
Organic matter can turn into the gas carbon dioxide.
Nutrients and Minerals are taken up by plants and can drain into groundwater.
Translocations are movements within the soil.
Gravity pulls water down from top to bottom.
Evaporating water draws the minerals up from the bottom to the top.
Animals living in the soil move the soil around in every direction.
Transformations occur when something changes into something else.
Humus is what is left when dead leaves decompose.
Weathering causes hard rock to erode and turn into smaller and smaller pieces of rock.
Oxygen reacts with the minerals such as iron which can make the soil look a reddish, ‘rusty’ colour.
All four processes are taking place at the same time!
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