The earth’s crust was- made up of rocks, as time passed due to disturbances like strong wind, rain etc. these rocks broke into tiny particles. The rocks keep on breaking all the time taking the space of pebble, sand and gravel. These tiny particles mixed with and animal remains formed the Soil.
The rocks break into smaller particles with the help of wind, water, heat and cold.
When the wind blows against a rock the softer layers wear off. This leaves holes and cracks in the rocks. As the wind continues to blow the softer layers are removed and the holes become bigger. Finally the rocks are reduced to smaller particles.
Moving water carries smaller pieces of rocks. These rocks hit against large rocks treating them down to smaller pieces.
Rocks get heated up when the climate is very hot. If those hot rocks get cooled suddenly, they crack, giving rise to smaller pieces.
Collect samples of soil from different places like a field, garden, river bank and the side of a pond. Note down the color of each sample of soil.
Now feel the soil with your fingers. What do you find? Different samples of soil have different colors. The smoothness of the samples is also different. One sample may be smooth whereas the other may be rough.
Layers of soil
Crops grow in the upper layer of soil, is called Top soil. Farming is done well where the top soil is rich with humus.
If you dig the top soil you will come to a layer where the particles are closely packed. This layer has rocks. It is the sub soil. Below the subsoil you will find solid rocks. These rocks break to form the sub soil.
Kinds of soil
There are four main kinds of soil. This depends upon the quantity of gravel, sand and clay present in the soil.
Gravel: Have very large particles. It has very little clay this soil cannot hold water.
Sand: Have smaller particles than gravel. It has very little humus. There is a lot of air in between the particles. It is rough in ouch and light brown or grey in color. It cannot hold much water.
Clay: is made up of small particles. These particles are smooth to touch. The particles are closely packed and do not allow the water to pass through easily.
Loam: it is the best soil for the growth of plants. It is a mixture of sand and clay. It is rich in humus. Loam has enough air and water for the proper growth of plants.