Physical Environment: Our Basic Life Support System.

Our Physical Environment

(The physical environment provides the essential background for all human activities on Earth)

Spheres of Earth

Our existence depends on the basic geological processes that govern the dynamics of the land surface and vast bodies of water. These, in turn, are controlled by the sun whose radiant energy drives the atmosphere and oceans as well as influence climatic patterns. As we know, we all live in natural landscapes that are shaped by glaciers, rivers, ground water and wind. So, we can say, physical environment is the basic life support system that provides the air we breathe, the water we drink, the food we eat and the land where we live. Then who are we? We are also belong to an environment which is known as Biological environment. Biological environment include not only humans but also animals, plants and other organisms. These two components i.e. physical and biological environment are interdependent. Components of environment are not static. They are going through several process of change. Broadly, the environment can be divided  into four spheres . They are Lithosphere, Atmosphere, Hydrosphere and Biosphere. In this article, I am going to discuss some basic concepts in lithosphere.

Lithosphere

Till date it is not possible for humans to know that how exactly the earth was formed several years ago. Geologists observed some geological processes like volcanic eruptions, earthquake waves, and some man made processes like deep mines operation and crustal boring. They concluded one thing from these observations. that is our earth must be distributed in the form of several concentric layers with different characteristics. 

Interior of the earth 

Chemical Composition

Geologists divided the earth into three layers according to the chemical composition. They are crust, mantle and core.

Crust: The outermost shell, called the crust is the thinnest layer. Its average thickness, however, varies from 5 to 40 kilometres. The average thickness of the crust beneath the ocean is 5 kilometres on the other hand the continental crust on an average is about 40 kilometres thick. Despite greater thickness, the continental crust is less dense than the oceanic crust because it is made of a mix of light and dense rock types. The oceanic crust is composed mostly of dense rocks such as Basalt. Hence, these rocks settle at a lower level than the rocks of the continental crust.

Mantle: The next layer mantle is separated from the curst by a boundary called Moho discontinuity. (It is named after the geologist Mohorovick). The mantle is about 2900 kilometres thick. It is divided into two sections: the upper mantle and the lower mantle.

Core: The innermost layer is core. Being composed of mostly metal, it is also known as the metallic core. It is separated from the mantle by a boundary. The core is divided into two parts. The outer core is composed of Iron and is in liquid state. The inner core is composed of Iron and nickel. The extreme pressure exerted by the weight of the overlying rocks keeps the inner core solid. Temperature and pressure inside the earth increase with depth. The density of rocks also increases as we go down from the surface to the core of the earth.

Mechanical Composition

The layers of the earth may also be grouped according to their consistency or mechanical composition. They are Lithosphere, Asthenosphere, Mesosphere and Barysphere. 

Lithosphere: The lithosphere is the solid layer composed of the crust and the upper mantle. It floats on the asthenosphere, which is a 100 kilometres thick layer found at the top of the lower mantle. The most abundant elements of the lithosphere on the earth’s crust are oxygen, silicon, aluminium, and Iron. Some of the metals formed by the mixture of these elements. They are

Quartz = Silicon + oxygen.

Feldspar = Silicon + Oxygen + Potassium + Aluminium.

Iron oxide = when oxygen is bonded with Iron.

Aluminium oxide = when oxygen is bonded with aluminium.

Asthenosphere: In asthenosphere, due to high pressure and temperature, some melting takes place. It makes the asthenosphere a bit softer than the rest of the mantle. it is the semi liquid asthenosphere, which enables the lithosphere to move around.

Mesosphere and Barysphere: Below asthenosphere, the layer upto mantle is mesosphere in earth's zone whereas the whole core is termed as Barysphere.

Upper layer of the earth

The upper layer of the earth consisting of rock materials, extending both over the continents and ocean basins is known as Lithosphere. Rocks rich in silica and aluminium, called 'Sial' layer, found over the continents. In the ocean basins, the rocks are mainly rich in silica and magnesium, called 'Sima'. Then what are rocks and how many types of are they? 

Rocks are the solid mineral material forming part of the surface of the earth, exposed on the surface or underlying the soil. On the basis of the origin, rocks may be igneous, sedimentary and metamorphic.

Types of Rocks

Igneous rocks: Due to very high temperature deep inside the earth, materials are in molten state. They are called magma. When this magma reaches the earth’s surface it is called lava. Cooling of magma either inside the earth or above it results in the formation of hard solid igneous rocks. ‘Igneous’ is derived from a Latin word ‘ignis’ meaning ‘fire’. As the name suggests, these rocks are formed from hot molten lava or magma. They make up about two-third of the earth’s crust. So they are also called primary or basic rocks. Granite and Basalt are examples of igneous rocks.

Sedimentary rocks: Basic rocks are broken into small pieces in many ways and form sediments ranging from gravel to sand, clay and silt. Sediments as well as organic remains are deposited in layers in low-lying areas. They get compressed and cemented together to form sedimentary rocks. Most of the rocks on the earth’s surface are sedimentary rocks. These rocks are soft and break easily. Limestone, conglomerate, sandstone, shale and coal are examples of sedimentary rocks.

Metamorphic rocks: Due to pressure and heat, chemical and structural changes take place in the existing rocks i.e. both igneous and sedimentary. Chemical changes lead to recombination of elements and thus totally new minerals are formed. During structural changes, more compact mineral patterns or different forms of crystals are formed. Rocks thus formed are completely different in appearance and characteristics from the original rocks. They are known as metamorphic rocks (‘Metamorphosis’ means a change of form). Gneiss, slate, marble and diamond are some examples of metamorphic rocks transformed from granite (means an igneous rock), shale, limestone and coal (sedimentary rocks) respectively.