The Environment

Date: January 23, 2018

Environment Biotic and Abiotic factors Atmosphere Hydrosphere and Lithosphere

The Environment

The sum of biotic (non-living) and abiotic (non-living) factors that surround and influence an organism is called Environment. Principally there are various physical attributes to environment called as physical environment which are comprised of hydrosphere, atmosphere and lithosphere. All these have influence on an organisms and in reciprocation, organism too influence the environment by various activities involving death and decay of organic matter.

  1. Atmosphere: The outer layer of earth’s surface is known as atmosphere. It is divided into a series of concentric shells or spheres due to variations in temperature and pressure at various altitudes. These layers are: troposphere, stratosphere, mesosphere and thermosphere (also known as ionosphere) as illustrated in Figure 1.
  • Troposphere: his is the lowest part of the atmosphere - the part we live in. It contains most of our weather ex. clouds, rain and snow. This also contains 75 % of all atmospheric gases. In this part of the atmosphere the temperature gets colder as the distance above the earth increases, by about 6.5°C per 1000 meter elevation. The transition part between troposphere and stratosphere is referred to as tropopause.
  • Stratosphere: This is the second atmospheric layer which extends up to 50 km from troposphere. This atmospheric zone contains ozone layer which is required for absorption of UV radiations from sun and their conversion into energy. In the lower part of stratosphere, commercial passenger jets fly. Unlike troposphere, in this atmospheric layer, towards elevation temperature increase.
  • Mesosphere: The layer above stratosphere is mesosphere and the transition layer occurring between the two is known as mesopause. It is extended up to 80-100 kms above the ground. In mesosphere most of the meteors gets burnt up. In this layer, as elevation is reached, temperature becomes colder. The air in the mesosphere is far too thin to breathe; air pressure at the bottom of the layer is well below 1% of the pressure at sea level.
  • Thermosphere: This layer is extended from 100-1000km above ground surface. This is also referred to as Ionosphere. High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere, raising its temperature to hundreds or at times thousands of degrees. However, the air in this layer is so thin that it would feel freezing cold to us! In many ways, the thermosphere is more like outer space than a part of the atmosphere. Many satellites actually orbit Earth withinthe thermosphere. Variations in the amount of energy coming from the Sun exert a powerful influence on both the height of the top of this layer and the temperature within it.
  1. Hydrosphere: Hydrosphere, discontinuous layer of water at or near Earth’s surface. It includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapour. Oceans, glaciers, lakes, rivers, estuaries etc constitutes water containing bodied of atmosphere and take active part in water cycle (Figure 2). Water is the most abundant substance at the surface of  About 1.4 billion cubic km (326 million cubic miles) of water in liquid and frozen form make up the oceans, lakes, streams, glaciers, and ground water found there. It is this enormous volume of water, in its various manifestations, that forms the discontinuous layer, enclosing much of the terrestrial surface, known as the hydrosphere.

Table 1: Resource: Elizabeth Kay Berner and Robert A. Berner, The Global Water Cycle: Geochemistry and Environment

Reservoir

volume (in millions of cubic kilometres)

percent of total

Oceans

1,370.0

97.25

Ice caps and glaciers

29.0

2.05

Deep groundwater* (750–4,000 metres)

5.3

0.38

Shallow groundwater (less than 750 metres)

4.2

0.30

Lakes

0.125

0.01

Soil moisture

0.065

0.005

Atmosphere

0.013

0.001

Rivers

0.0017

0.0001

Biosphere

0.0006

0.00004

Total

1,408. 7

100

 

  1. Lithosphere: The third part of physical environment is Lithosphere referring to the soil present over earth’s surface. Unlike two other constituents of physical environment (atmosphere and hydrosphere) alternation in lithosphere is very a very slow and gradual process and occurs only towards the upper most surface. A vertical section through different layers of the soil is called the soil profile. Each layer differs in feel (texture), colour, depth and chemical composition. These layers are referred to as A soil horizon is a layer generally parallel to the soil surface, whose physical characteristics differ from the layers above and beneath. Horizons are defined in most cases by obvious physical features, chiefly colour and texture (Figure 3). The uppermost horizon is generally dark in colour as it is rich in humus and minerals. The humus makes the soil fertile and provides nutrients to growing plants. This layer is generally soft, porous and can retain more water. It is called the topsoil or the A-horizon. The next layer has a lesser amount of humus but more of minerals. This layer is generally harder and more compact and is called the B-horizon or the middle layer. The third layer is the C-horizon, which is made up of small lumps of rocks with cracks.