Definition and Components of Environment
Environment refers to the external physical, chemical, and biotic conditions surrounding an organism. The environment can be divided into four major components, which are interacting spheres viz. lithosphere, hydrosphere, atmosphere and biosphere.
Lithosphere
Lithosphere is the outermost layer of earth called crust, which comprises different landforms, minerals, metals, rocks. Its depth can reach up to 100 kilometres and is found on both land (terrestrial crust) and oceans (oceanic crust). The main component of lithosphere is earth’s tectonic plates.
Hydrosphere
Hydrosphere is comprised of all forms of water bodies on earth including oceans, seas, rivers, lakes, ponds, streams etc. It covers 70% of earth’s surface. 97.5% of water found on Earth is in the Oceans in the form of salt water. Only 2.5% of water on Earth is freshwater. Of this 2.5% fraction, 30.8% is available as groundwater and 68.9% is in frozen forms as in glaciers. Amount of 0.3% is available in rivers, reservoirs and lakes and is easily accessible to man.
Atmosphere
Atmosphere is gaseous layer enveloping the Earth. The atmosphere with oxygen in abundance is unique to Earth and sustains life. It mainly comprises 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and traces of hydrogen, helium, and noble gases. The amount of water vapour present is variable.
Biosphere
Biosphere refers to all the regions on Earth where life exists. The ecosystems that support life could be in soil, air, water or land. The term Biosphere was coined by Geologist Edward Suess who used this term for place on Earth where life can be found. Biosphere refers to the sum total of all living matter, the biomass or biota. It extends from the polar ice caps to the equator, with each region harbouring some life form suitable to the conditions there.
Within each sphere and between spheres, complex interactions and processes take place that govern environmental stability. Changes to one sphere often impact the others.
