Where does soil come from ?
| Most soils were originally created through the breaking down of the solid rock which, at one time, formed the earth.
On the surface of rock, water (which is essential for plant life to exist) evaporates quickly, so plants cannot survive unless they are very primitive, like lychen. |
Lychen on rock surface |
|
| Many things caused the rock to break down. |
Frost shatters rock |
For example, when water collects in rock crevices, it expands with tremendous force when it freezes. This can cause large rocks to shatter into fragments. |
|
| This leaves scope for simple plants like lychen, and more complex ones like moss to establish in the damp crevices. The plant roots also plunge deeper into the cracks forcing the rock further apart, and yet more water to accumulate. |
Moss grows in rock crevices |
|
Water grinds rock to sand |
Water is another weathering agent. Fast flowing water in rivers and streams grinds rock to pebbles and fragments that become sand. It can also carry them for considerable distances.These grinding down processes have been going on for millions of years. |
 |
It is no accident that some of the most productive soils in the world are associated with river valleys. |
|
| Perhaps early soils were made up of gravel sized particles. These would not support plant life very well, because they would not be able to hold much water.
|
Top of  this page |
In dry periods plants would die. When this happened, it added a new element to the soil ... the dead plant remains. |
| This new material was very different from the ground-up stone particles because it was organic.
It could act like a sponge, soaking up water in the soil when the weather was wet, and giving it off in dry periods. |
 |
 |
This made it easier for the next generation of plants to survive, and so the process continued over time, with the rock fragments getting smaller, and the organic matter content increasing, until soils something like the ones we see today were formed |
Top of this page
Where does soil come from | The mineral particles | The effect of particle sizes | Organic material | Soil inhabitants | Soil analysis | Soil composition | Characteristics of different soils
soil@hostweb.org.uk
Copyright © 1998 Fred Moor
|
|
![[Formation]](images/formbutt.gif){kind=small}