Components of Environment

The components of the environment are the atmosphere, hydrosphere, lithosphere, and biosphere.

1. Structure of Atmosphere: The layer of air surrounding the earth is the atmosphere. The atmosphere mass is about 5×1018 kg, 75 percent of which is limited to about 10km. The atmosphere thins out with increasing altitude, with no distinct boundaries. The Karman line at 100 km is often used as the partition between the atmosphere and outer space. Several layers can be distinguished in the atmosphere, it is based on composition and temperature variation. Atmosphere science or aerology is the study of the earth’s atmosphere and its processes.

Starting from the ground level is the troposphere which varies between 8 and 12 km in thickness. It is thin at the poles (8 km) and thicker at the equator (18 km). Typically air is composed of nitrogen (78.08%) oxygen (20.95%), argon(0.93%), carbon dioxide (0.031%) along with water vapour xenon, helium, krypton, xenon, hydrogen, methane, nitrogen-monoxide, ozone, etc. Warm air being lighter near the surface of the earth can readily rise above.

The molecules can travel to and from the troposphere in just a few days. Such vertical movement or convection of air produces clouds and rain and gives rise to most of the weather conditions. Temperature decreases with an increase in altitude in the troposphere till people reach the topmost layer or tropopause. Temperature decreases at a rate of 6.5°C for every 1 km, which is known as the Environmental Lapse Rate. Tropopause may reach a temperature of -55°c at the poles. Sometimes the temperature increase with altitude in the troposphere, giving rise to a situation called temperature inversion. Such conditions restrict the vertical mixing of air and reach air pollution incidence at ground level.

2. Structure of Lithosphere: The diameter of the earth is about 12700 km. The temperature and pressure penetrate deeper and deeper. The core temperature is assumed to be 5000 – 6000°K. Our earth comprises three concentric regions:

  • The core of approximately 7000 km in diameter is divided into the inner core and outer core. The solid inner core has a radius of 1216 km and a density of 13 grams/cc. The liquid outer core has an average thickness of 2270 km and a density of 11 grams/cc. The core is supposed to be composed of an iron and nickel alloy. About 10% of the layer is supposed to be composed of sulphur and oxygen as these elements are abundant in the cosmos and dissolve readily in molten iron.
  • The middle layer is the mantle which is about 2900 km thick. The upper mantle of 660 – 670 km thick from the base of the crust, and mostly contains olivine and pyroxene minerals. The asthenosphere lies at a depth of 100 -200 km from the earth’s surface. It’s a weak and deformed layer that acts as a lubricant for the plate tectonics to glide and may extend up to 600 km. The lower mantle stretches from 670 km to 2900 km below the earth’s surface. The lower mantle probably comprises silicon, magnesium, and oxygen along with some iron, calcium, and aluminum.

3. Structure of Hydrosphere: Water is found in the hydrosphere, lithosphere, and atmosphere and in almost everything including our body cells. It is an oxide of hydrogen and serves as one of the sources of hydrogen and oxygen in metabolisms. Its physical and chemical properties make it unique. It is present as water vapor in the atmosphere which takes part in the formation of clouds and fogs thus regulating our weather conditions.