The soil of the Earth

Whenever you look around or walk outdoors, or even when you have a fall, you are dealing with the Earth which we are all standing tall on.

But, did you ever think about how the ground and the rest of the Earth has been created? In short, have you ever given any thought to 'soil', which is something that we see every now and then and which is also the material that most of the things around us are made of? Soil...this is exactly what today's article is about.

What exactly is soil?

This question can be answered in a very simple or very complicated way. In simple terms, soil is the loose, upper layer of the Earth's crust. In technical terms, soil is what makes up the Pedosphere.

The Pedosphere is what lies between the Lithosphere and the combined layer of the Hydrosphere, Atmosphere and Biosphere.

By now you should know what the Lithosphere is, since it was mentioned in the last two Geo Facts articles. However, just to refresh your memory, the Lithosphere is the hard rocky outer layer of the Earth.

The Hydrosphere, Atmosphere and Biosphere, in simple terms, are the water, air and life on the surface of the Earth. Soil covers a large portion of the Earth's land surface. It is an important natural resource that either directly or indirectly supports most of the planet's life.

If we think about this for a moment, we can see that life on Earth depends upon soil for food. Plants which are rooted in the soil get the necessary nutrients from the soil and animals get their nutrients from plants or from other animals that eat plants. Soil is a mixture of mineral and organic materials along with air and water.

The contents of soil are never the same in different locations and is always changing. There are many different kinds and types of soils and each has certain characteristics including a specific colour and composition.

Different kinds of soils support the growth of different types of plants and also determine how well that plant life grows. Soil is formed slowly, but can be easily destroyed. Therefore, soil conservation is important for continued support of life.

How is soil formed?

Earth is rocky where its few outer layers are concerned. Therefore, the scientific theory suggests that soil is formed out of rock after being broken up in to tiny paticles over time.

Many conditions affect the formation of soil out of rock, such as heat and cold, attack by wind, rain, hail and ice. Furthermore, the massive forces of water which are present when water is expanded into ice make solid rock shatter into smaller pieces. But, however small these fragments may be, they still have the same properties as the parent rock.

So, how would soil change in composition from place to place? So far, we have delved only into soil being formed out of a parent rock. But, other than that, there are five more factors which affect soil formation such as time, climate, atmospheric composition, topography and organisms.

The first three factors are obvious. Topography means how different features in a landscape are arranged. These features might be things such as the geographical settings and even things such as vegetation, human-made features and culture.

Organisms which affect soil would be anyone ranging from micro-organisms such as bacteria to macro-organisms such as all the animals we come across.
 

Soil structure

By now you know that soil is made up of rock. When this happens, the layer of soil resides on top of the rocky layer. This layer of soil can be broken down further into a few more layers as follows. Note that only the main layers are shown here and in some situations, intermediate layers have been defined as well.

* O-Horizon

This is the outermost layer of soil which consists mainly of organic matter from the vegetation, which are accumulated under conditions of free aeration (exposed to air).

* A-Horizon

This layer, which is below the O-Horizon, is also known as the plough zone since it is very rich in organic material, and suits cultivation. This is made up of mineral matter mixed with some decomposed organic matter.

* B-Horizon

Residing below the A-Horizon, this layer is made up of clay, iron or organic matter. Some limestone may also accumulate in this layer.

* C-Horizon

This layer has very little life compared to the upper layers. The level of micro-organisms is low, and the composition is very close to the parent material.

* R-Horizon

This is the last layer of soil, which in fact is more of the parent material itself.

Compiled by Aravinda Dassanayake