The Earth
The Earth has only one natural Satellite (The moon). It is the only planet with adequate water and air around it. Its temperature is also very suitable for flora, fauna, aquatic and human life.
The shape of the earth is almost spherical, flattened a little at the poles with a slight bulge at the equator.
The Internal structure of the earth consists of three layers – the crust, mantle and core the core consists of two distinct phases– lnner core (Solid) and outer core (liquid).
The crust : It is the surface layer of the Earth. It is thin and brittle. It has two different regions – oceanic Region (Crust) and continental region (crust). These are less dense than the mantle and they float atop the mantle because of the low density it contains lighter element than that of the mantle rock.
The Mantle : It is rocky and contains heavier elements than that of curst rock. Almost 82% of the Earth’s volume and 65% of the mass is composed of the thickest layer of denser rock (mantle).
Lithosphere and Asthenosphere are the two Zones of the upper mantle.
Lithosphere : It is a stiff, cool and relatively breakable uppermost Zone similar to that of the crust, found directly beneath the surface of the crust.
Asthenosphere : It is a Solid (though flows very slowly) layer of mantle found beneath the lithosphere. The rock becomes more rigid beneath the asthenosphere and it extends upto the remaining 2200 km of lower mantle.
The Core : It lies at the centre of the earth. Almost 15% of the Earth’s volume and 30% of its mass is occupied by the core. It consists of two layers and is nearly twice as dense as the mantle. It is due to the fact that the core of the Earth is largely made of metallic iron.
The Inner core: It is as hot as the surface of the sun. It is solid as melting is prevented by the intense pressure from the weight of the earth above.
The outer core: It allows the iron and nickel to flow in a liquid phase due to the exertion of less weight. An electric current that creates Earth’s magnetic field is produced by the moving iron and other metals.
The central core of the Earth is mostly composed of iron. The crust is composed of mostly lighter elements. Oxygen constitutes almost half the mass of the Earth’s crust and Silicon about a fourth.
The Earth is believed to have originated Some 4,600 million years ago. Knowledge and comprehension of the age of each rock formation is very essential to understand the history of the Earth.
Relative Dating : It refers to the ordering of rocks in sequence by their comparative ages. It relates time relatively to other occurrences or happening associated with the Earth in the past.
Radiometric Dating : it refers to the measurement of the radioactive isotopes relative to the decay products. It is based on the assumption.
In order to increase accuracy cross checkings should be conducted for relative and radiometric dating.
The movements of the Earth are of two types : (i) Rotation/ daily Mation (ii) Revolution/Annual motion
The earth spins on its own imaginary axis line which runs North rock to South and passes through the centre of the Earth. It spins from west to east once in about 24 hours. Day and night occure due to this effect. We also experience change in the direction of wind and ocean currents.
The Earth also revolves around the sun along an almost circular path called its orbit. It is done along with the rotation on its axis. Change in seasons are caused by the revolution of the Earth. The annual motion of the Earth together with its inclined axis causes the four seasons of Spring, Summer, Autumn and Winter.
Equinoxes refer to dates when the nights and days are equal. The sun shines directly over the equator during these days. The equinoxes represent the midpoint in the shifting of direct rays of the sun between the Tropic of canner and the Tropic of Capricorn. 21 March is the spring equinox in the Northern Hemisphere and September 23 is autumnal equinox for the Southern Hemisphere.
Solstice refers to the time of the year when the difference between the length of days and the length of nights is the largest. The Sun shines vertically over a tropic during these days.
When the Earth Comes between the moon and the sun, The moon is said to be in eclipse. It is also known as the Lunar eclipse which occurs only on a full moon day.
When the moon comes between the sun and the Earth, The sun is said to be in eclipse and this is called solar eclipse A Solar eclipse occurs on a new moon day (not on every new moon day) when the moon is in line with the sun.
The surface of the Earth has 4 distinct spheres– Lithosphere, Itydrosphere, Atmosphere, and Bisophere
Lithosphere includes the land surface and the ocean floors.
Hydrosphere includes oceans, seas and other water surface.
Atmosphere includes the air surface.
Biosphere is spread over all the above three spheres where life exists.
Lithosphere is the topmost crust of the Earth comprising soil, Sand and rocks which have come from ancient rocks that have crumbled down over thousand of years under the impact of heat of the sun and cool of the rains. Rock are composed of minerals – natural inorganic substances. Rocks of the Earth’s crust are grouped in the following three classes.
(i) Igneous Rocks
(ii) Sedimentary Rocks
(iii) Metamorphic Rocks
Igneous rocks are those which are solidified directly from molten materials. These are commonly referred to as extrusive rocks and intrusive rocks. The extrusive rocks are solidified at the surface (lava and pumice). The intrusive rocks are solidified beneath the surface (granites).
Sedimentary rocks are formed from material / deposits created by chemical action. Conglomerates are the rocks formed by the deposition of sediment in water. Coals are the Rocks formed by the deposition of organic matter.
Metamorphic Rocks are originally igneous or sedimentary but have been transformed by pressure, heat or action of water. Limestone a sedimentary rock may turn into marble under intense heat.
The land surface of the Earth is divided into sever continents–
(i) Asia
(ii) Europe
(iii) Africa
(iv) North America
(v) South America
(vi) Antarctica
(vii) Australia
Hydrosphere includes the water of the atmosphere as well as the water on the surface of the earth which includes the water of the oceans, rivers, ice-sheets and ground water. The water in the oceans is more than 97 percent of world’s total water, Glaciers, ice and Snow fresh water lakes, rivers and the underground water constitute the rest of the water resources.
The entire atmosphere is mixture of gases. It is essential for life on the Earth. The general circulation of atmosphere redistributes heat on the globe. The atmosphere air is composed of about 78% nitrogen and 21% oxygen. There are also other grass like argon, helium, hydrogen, methane, carbon dioxide etc. It also contains tiny Particles of dust and some other substances . It also contains varying anounts of water vapor.
Oxygen and carbon dioxide in the atmosphere are necessary for sustaining the fauna and flora. The amount of carbon dioxide varies from place to place.
Biosphere refers to the living world and extends to any place that life can exist on Earth. The major factor which affects the life in the Biosphere is the distance between the Earth and the Sun. The tilt of the earth which influences the season and climate is also important. The Biosphere includes all living organisms together with the dead. Organic matter produced by them. It helps to drive the global bio-geochemical cycle. It can be called the global ecosystem which is comprised of the totalty of biodiversity on earth.
The Zones of the Earth
Torrid Zone : It is the hottest Zone. It lies between 23½° north and 23½° south North temperate zone: It has a marked annual range of temperature. It lies between 23½° North and 66½°North.
South Temperate Zone : it has also a marked annual range of temperature. It lies between 23½° South and 66½° south
North Frigid Zone : It is extremely cold throughout the year. It lies between 66½° North and 90° North.
South Frigid Zone : It is also extremely cold throughout the year. It lies between 66½° South and 90° South.
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