The Origins of Soil
Whenever we talk about cultivation or gardening we are constantly referring a matter called ‘soil’. But what is it and where does it originate from? Soil originally was formed from plant and animal decay. Billions of years ago, great masses of rock were crumbling under the massive pressure created by heat, water and subsequent friction. When millions of rock masses clashed with each other, bits of rock were strewn, small pieces of rock combined together to form larger rock pieces while some dissolved in water. Time of total chaos, as one can imagine.
Helped by the enormous gaseous exchange which was all around the earth there were tremendous temperature variations. This alternating heat and cold created havoc when rocks and stones crumbled and everything around went through a complete upheaval. This is the time when the earth was born. Imagine the havoc created by little temperature variations in our every day life – with the sudden freeze and thawing, water pipes bursting. Now imagine this havoc multiplied by several billion times. You can picture this presumably.
From these series of rubbing against each other, stones crumbling under pressure, it is easy to imagine how sand was formed. This is one of the layers or types of the soil – the sandy soil. You see great stretches of sandy soil in sea beaches. Come to think of it, if the earth only had sandy soil, it would be highly unproductive. But the early forms of plant and animal life, when dead, decayed to form rock mass and another type of soil emerged. Thus when we speak of soil, it could be a mixture of sandy soil, which could have sand, clay, vegetable matter or humus and sometimes animal waste as its constituents.
This brings us to another type of soil called the clayey soil. Some of the rocks, billions of years ago dissolved in water, as it covered it. This was aided by extreme temperatures and a gaseous substance in the air called carbon dioxide or carbonic acid. This gas can corrode rocks and eat away some of the elements in the rock. You have surely seen some large rock formation where one portion seems to be eaten away and juts out as if it has been broken off by some force. This is the effect of this corroding gas. This ‘eaten off’ part then changed into a substance which we call ‘clay’. As is evident this changed form is a result of not a mechanical but a chemical process.
The difference of the origin of sand and clay is thus: while sand was formed as a result of a mechanical process, clay was a result of a chemical reaction. The difference is also in the quality of the end result. An example of a purely mechanical process can be given if think of a large lump of sugar. When you break it into very tiny pieces, the components are still sugar. Sand from rock mass is pretty much the same. On the contrary, chemical changes can completely alter the end product. For instance, the rock through chemical processes turned into clay, an otherwise completely foreign substance. Thus a clayey soil is often referred to as mud soil because of the water content in its formation.
There is another type of soil called the lime soil. If I tell you now that farming soil was originally made from limestone, the expected question would be: from where did limestone turn up suddenly? Again, going back to the origin of earth, there were millions of animals belonging to the lower strata in the overall hierarchy of the animal kingdom who absorbed water particles of lime. This lime was subsequently used to make their skeletons and homes which they made to protect themselves from larger animals of prey. A coral under the sea is a perfect example of skeleton forming animal.
With time, the animals died and decayed but their skeletons remained. When large masses of such skeletons were pressed together over millions of years, limestone was formed. Examples of limestone are marble, a crystalline type of limestone, chalk, etc. You can tell whether it is limestone, if you drop a bit of this acid on some lime. See the effervescence. Then try it with chalk or marble. The same fizz occurs here too. No special acid test is required, but ordinary household vinegar can give you the same result.
Thus these are the three types of soil which a vegetable grower has to deal with.