Earth’s zones


The earth In each hemisphere is divide into three different zones: (a) frigid zone, (b) temperature zone and (c) torrid zone. The frigid zone exists above 660 30’ latitude in both hemispheres. The temperate zone exists between 23o30’ to 66030’ latitude and the torrid zones exits below 23030’ latitude in both hemispheres.

The evolutions of the continents



The shape of the earth’s surface has been charging over the time. The different continents of the earth had a single landmass in the beginning. The single landmass was called pangaea and surrounding ocean called panthalassa. The pangaea split into two major continental groups- laurasia and gondwanaland about 180 million years ago.
The southern landmass, gondwanaland, further broke up isolating india and antarctica-australia. South america similarly drifted away from africa. The sediments of the shallow sea ‘tethys sea’ between India and africa northwars. the himalayas emerged as a result of this process.
However, plate tectonics theory argues that earth’s crust is made up of a series of rigid plates that float on a soft layer of the mantle and are moved about by convection currents in the earth’s interior. These plates converge and diverge along margins naked by earthquakes, volcanoes and other seismic activities. Plates diverge from mid-ocean ridge where molten lava pushes upward and forces the plates apart a rate of about 30 mm per year. While converging, the oceanic plates below the lighter continetal rock.

The earth’s atmosphere


The earth is surrounded by a layer of air, which is called the atmosphere. It reached to 560km from the surface of the earth, so we are only able to see what occurs fairly close to the ground. The atmosphere consists about 77% nitrogen , 21% oxygen, with traces of argon, carbon dioxide and water. The atmosphere of the earth can be divided into several distinct zones, as shown in the figure.
The atmosphere is where all weather takes place; and extended from 8 to 14.5 km above the surface of the earth. The air pressure at the top of the troposphere is only 10% of that at sea level. Above the troposphere is the stratosphere and extend to 50 km, where air flow is mostly horizontal. The thin ozone layer in the upper stratosphere has a high concentration of ozone . this layer is primarily important as it absorbs the ultraviolet radiation from sunlight. The mesosphere is above the stratosphere and extends to 85 km. above the mesosphere is he thermisphere and extends to 600 km, where many atoms are ionized. The ionosphere is very thin, but it is where aurora takes place,and is also responsible for absorbing the most energetic photons from the sun. the exosphere starts at the top to the thermosphere and continues until it merges with interplanetary gases, or space.

the earth’s interior structure


the earth is made up from several layers like union. These layers can be broadly divided in to three types. These are crust, mantle and core. The srust is the outer layer of the earth where we live. The crust varies considerably in thickness from 5 km in oceanic regions to 70 km in the Himalayas. It is thinner under the oceans and thicker under the continents. The crust is made up solid rock and divided in to several plates. These plates float around independently on top of the hot mantle below. The mantle is found below the crust.
Most of the mass of the earth is in the mantle. The thickness of mantle is about 2900km. magma is generated by melting of the mantle. He core found below the mental can be further divided in to two parts i.e. outer core and inner core. The outer core creates the earth’s magnetic field. It is huge magnet in the center of the planet. The core is probably composed mostly of iron. The inner core and crust are solid; the outer core and mantle layers are plastic or semi-fluid.
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