Definations :
The origin and evolution of earth is best explained by ‘Planetesimal Hypothesis’ put forth by T.C. Chamberlain and F.R. Moulton in 19t h century and Nebular hypothesis.
The origin and evolution of earth is best explained by ‘Planetesimal Hypothesis’ put forth by T.C. Chamberlain and F.R. Moulton in 19t h century and Nebular hypothesis.
According to ‘Nebular Hypothesis’:
1. Whole solar system at one time is a cloudy (nebula) mass of matter in form of vapor or gas.
2 . It was intensely hot and incandescent. It was in perpetual motion.
3. On lapse of time nebula began to cool and the vapors in the outer layer are condensed and thrown out in the form of rings. Further condensation and disruption lead to formation of planets.
4 .The central mass which is still incandescent and not yet condensed is ‘SUN
Spheres of Earth
Geographically EARTH constitutes of three spheres corresponding to three states of matter (Solid, Liquid & Gas)
The solid zone is Lithosphere. The incomplete covering of water forming seas and oceans (liquid spheres) is Hydrosphere. The gaseous envelop over the earth surface is Atmosphere.
Atmosphere:
– The atmosphere forms an envelop, 322 Km over the earth’s surface. This envelop of air that covers both lithosphere and hydrosphere is called atmosphere. It contains water modules and dust, which act as nuclei for the condensation of water vapour to form cloud or fog.
N2 – 78.054 % O2 – 20.946 %
CO2 – 0.033 % Argon – 0.934 %
In addition, inert gases such as helium, neon, krypton and xenon are present. The water vapor content in atmosphere varies from place to place and time to time.
Air becomes less dense with height until it gets too thin to support life. Atmosphere contributes only 0.03 %
weight to the earth.
Hydrosphere
1 Covers almost 3/4t h of earth crust.
2 The Hydrosphere is 10 Km deep and occupies 70 % of earth’s surface.
3 Hydrosphere makes only 6.91 % of the earth mass but by volume 15 times than that of
the visible land above the sea level.
4 It contains absorbed air and carries particles of rocks as sediments.
5 Most of it lies with in the ocean basins and also appears on surface of land in the form
of rivers, ponds, lakes and as ground waters.
6 The quality of different waters, varies
