THE LITHOSPHERE

Neil Gabriel Esgra

The Lithosphere

The lithosphere (from the Greek [lithos] for "rocky" + [sphaira] for "sphere") is the rigid outermost shell of a rocky planet. It comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.

http://en.wikipedia.org/wiki/File:Earth-crust-cutaway-english.svg

Earth's Lithosphere• In the Earth, the lithosphere includes the

crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle.

• The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process is called the pedosphere.

two types of lithosphere

• Oceanic lithosphere, which is associated with Oceanic crust and exists in the ocean basins

• Continental lithosphere, which is associated with Continental crust

Soil

A Natural Resource

Soil is one of the most important and essential natural resources. Farmers and gardeners know this fact and go to great efforts to conserve it. They understand that when the soil is destroyed, then gardens will not be successful and good crops cannot grow. They also know that it takes a considerable amount of time for soil to form.

Soil is defined as a covering over most of the earth's land surface. It is made of particles of rock and minerals, living things and the remains of living things. It takes thousands of years for soil to form just a few inches and for some parts of the country it has been less than that.

Soil is formed in two general ways:

When weather conditions cause rock to break down.

When soil is carried from one place to another.

How is soil made?

• Air Moving air, such as the wind blows sand against rock to wear it down.

• Water The force of running water can wear away rock. Rain and snow also help to break down rock into smaller particles.

• Plants Plants help the soil as they grow and when they die. As dead plants decay, it adds an organic material to the soil, which makes it more fertile.

• Animals The body waste of many animals helps to keep the soil fertile, as well as the remains of dead animals as they decay.

Soil is a natural resource, which is required for production of food, industrial raw materials as well as for generation of energy resources. It is also a natural value, which is protected as natural heritage. From the viewpoint of natural resource, natural value and spatial factor it is irreplaceable for development and existence of mankind.

The preservation of the natural resource soil from physical destruction and pollution as well as the preservation of balance between the soil and other parts of the ecosystem represent one of the significant activities in the world nowadays.

Soil degradation: The antropogene destruction of the soil results from intensive construction of motorways and other infrastructural buildings in the area where soil degradation means its physical destruction due to construction of motorway structures, dams, cuttings and junctions.

Acidification and salinization of the soil: the soil developed on the bases containing a lot of cations, some of them also a lot of carbonates. The buffering capacity of such soils is large, therefore no essential changes in the pH value are expected. The soil on noncarbonate (silicate) bases is more strongly exposed to acidification. The same can be maintained for the washed out soils on deep decalcified depositions.

Soil pollution: There are some areas, which are rather heavily polluted in the world. In the past, the main polluters were metallurgic plants, chemical and processing industry - industrial pollution. The densely populated parts of the country and extensive daily labor migration contribute to the soil pollution - urban pollution. Intensive processing of food can also have adverse effects on the environment and soil system - plant - underground water what can be defined as agricultural pollution.

Soil Erosion

Soil is formed as a result of weathering of rocks. There are also many living organisms in the soil. Soil is, in fact a product of the interaction of living organisms with rocks. Soil has many layers. The topmost layer is called the topsoil and is the most fertile. The removal of this topsoil is called soil erosion.

Effects of Soil Erosion• Soil erosion results in the loss of soil

fertility and makes the land barren. There are more than 25 million hectares of barren lands in the world now.

• Soil erosion also leads to desertification. Desertification refers to increase of desert areas.

Causes of Erosion

• The main cause of soil erosion is the removal of vegetation. Vegetation removal takes place due to removal of forest covers. Unscientific farming has also led to barren lands.

• The removal of vegetation exposes the topsoil to water and wind. Water and wind cause the topsoil to be removed.

Water Erosion

Removal of topsoil by water is called water erosion. It takes place in the following ways:

• Sheet erosion• Rill erosion• Gully erosion• Riparian erosion• Wind erosion

• Gully ErosionDeep depressions called the gullies are formed by swiftly moving waters causing soil erosion by them.

• Riparian ErosionThe banks of rivers lose top soil due to the action of the fast moving rivers waters. These waters remove the underlying soil and this results in the loss of topsoil.

• Sheet ErosionThe removal of the entire topsoil as a result of heavy rains is called sheet erosion.

• Rill ErosionRunoff water moves across the soil forming small streams. The topsoil is removed only in these rills formed by the water streams.

• Soil LeachingThe topsoil is fertile due to rich presence of minerals. Sometimes the rain water dissolves these minerals which go down into the soil along with the water. This results in the loss of fertility of the topsoil.

Wind ErosionThe other cause for erosion is wind. It is more in areas where there is less or no vegetation covering the land. The fast moving wind moves the fine particles to other places. The deserts are encroaching the fertile areas in this manner. The wind laden with fine sand deposits the latter and forms sand dunes. Shifting sand dunes are common in dry areas of Rajasthan, Gujarat and Madhya Pradesh. Expansion of deserts in this manner is called desertification.

Prevention and Control of Soil ErosionIncrease of VegetationWhen the land is covered with vegetation, the roots of the plants and trees interlock and interlace to bind the soil particles. This helps in two ways:

• does not allow the soil particles to be carried away by wind or water

• does not allow free flow of water over the soil which prevent erosion of soil by flowing water

Several methods can be employed to increase the vegetation cover of land. Some of them are as follows:Crop RotationThe practice of growing different crops at different times on the same land is called crop rotation. This keeps the topsoil covered with vegetation. Rotation of cereal crops with legumes also keeps the soil enriched with nitrogen (from the legumes).

ReforestationSlopes are more subject to soil erosion by running water. Growing trees on lands which have lost their vegetation is called reforestation. Trees like Albizia, Cassia, Butia, etc. are suitable for this.Strip CroppingIt involves growing of crops in strips. The most common method followed is the contour farming where the strips of crop are at right angles to the slope. Wind-strip cropping is when the strips of crop are place at right angles to the direction of wind.

Restoring Soil FertilityFertile soil supports vegetation. Loss of fertility results in loss of vegetation and this exposes the land to erosion. Fertility of soil can be increased by addition of natural and synthetic fertilizers.Control of GrazingCovering the land with small plants and grasses helps the topsoil to remain in place as the roots of these plants bind with the soil particles. Cattle graze on these plants and expose the topsoil Thus, grazing should be allowed only on the land meant for the purpose and other areas should be protected from grazing.

TerracingFields are cut at right angles to the slope. This slows down the flowing water and allows it to irrigate the crops, as well.Dam BuildingWith the dams the speed and amount of water flowing can be controlled. This will control the soil erosion of the river banks.

Wind BreakersTrees are planted across the wind direction to protect against the high velocity winds. These rows of trees are called shelter belts or wind breakers.