"Rain, wind, sun, and ice all help convert rock to soil, but it is the living creatures that clearly make the soil hospitable for other living forms."
How is Soil Formed and How Long Does It Take?
Soil formation is a long slow process. It's estimated that an inch of soil takes 500 to 1000 years to form. Soil is constantly being formed. It is also constantly being eroded.
Stage One
This is the rock pulverizing stage. Here the forces of wind, rain, freezing and thawing water, earthquakes, volcanos all work to slowly pulverize rocks into smaller partcles that can make up a soil.
At the end of this stage we have most likely a combination of sand, silt and clay sized particles. These form a mineral soil like substance but are unable to support life.
They are missing nitrogen. It may seem nitrogen should be the least of a being's worries. After all the air we breath is made up of about 78% nitrogen gas. The problem is that plants can not use nitrogen in this form. For them it needs to be converted to either ammonia which is a combination of nitrogen and hydrogen or nitrates - a combination of nitorgen and oxygen.
Stage Two
This is the early stage of what we might call soil. Here we add some life, specifically lichens.
Lichens are a symbiotic relationship of algae and fungus. The algae has the very important role of fixing the nitrogen, changing it from nitrogen gas to a form the plant can use. It also captures the sunlight and creates sugars and oxygen. The fungus provides a place for the algae to live, along with water and the mineral nutrients it needs.
 | Here very old lichens begin the process of soil formation. This is in Churchill MB. |
Lichens are very long lived - hundreds to thousands of years and they also further break down rock with acids they produce. About 8% of the earth is covered by lichens.
Lichens are joined by mosses, bacteria, protozoa, and fungi. These form a complex cooperatve community that works to store nitrogen, nutrients and water to foster the growth of new plants.
Stage Three
At this time the little pockets of soil have formed to the extent that some larger plants, plants with roots can have a go at growing.
The first pioneers will be short lived but as their bodies are added to the layers of soil forming the soil becomes more capable of supporting life. Humus builds and soil horizons begin to form.
Stage Four
The soils are developed enough to support thick vegetation
