Earth

Earth

>> The largest of four planets of inner group solar system i.e. Mercury, Venus, Earth and Mars and third closest to the sun.

• Shape - spherical

• Polar radius - 21 km shorter than equatorial radius

• Average radius - 6378 km (3965 miles)

• Surface Area - 510 x 106 km2 (29% is land)

• Overall Density - 5.5 g/cm3

• Mount Everest is 8.8 km above sea level

• Ocean floor is an average 3.7 km below sea level

• Average height above sea level is 7 km

Principal Division of Earth

>> Consist of three:-

1) Atmosphere – Troposphere and Stratosphere

2) Hydrosphere

3) Lithosphere

(1) Atmosphere:

• Gaseous portion of the Earth extending upwards for hundreds of miles above sea level.

• It is a mixture of 98% nitrogen, 21% oxygen, carbon dioxide, water vapour and minor amount of other gases. The atmosphere is divided into two parts which is Troposphere and Stratosphere.

• Troposhere - the closest to the Earth ~ 13 km. It contains almost all of the water vapour, clouds and storms.

• Stratosphere - the overlying layer ~ 55 km above the surface, contains the ozone layer. It acts as an insulating agent protecting us from the heat and ultra violet radiation of the sun and makes possible the evaporation and precipitation of moisture and is thus of crucial important to organisms on surface of Earth.

• The atmosphere is an important geologic agent and is responsible for the processes of weathering which are continually at work on the Earth's surface.

(2) Hydrosphere:

• Total mass of water or the surface of our planet which includes about 98% of water in the oceans and 2% in lakes, rivers as well as ground water which exist in the pores and crevices of the crustal rocks and soils.

• 71% of Earth covered by oceans to average depth of 4 km. Water is essential to man and of geologic important.

• All of Earth's weather patterns, climate, rainfall and the extremely important carbon dioxide content of atmosphere are influenced by the seas and oceans.

• Hydrosphere is in constant motion - evaporating through atmosphere, precipitating as rain and returning to Earth.

• As water moves over the Earth's surface it erodes, transports and deposits weathered rock material, constantly modifying the Earth's landscape.

(3) Lithosphere:

• Lithos means rock.

• The solid portion of the Earth composed of crust and upper mantle.

• It is a layer of rocks about 70 km thick, that rests upon soft weak material and is broken into about 12 major plates which is slowly moved by the flow of material in a layer that directly underlies the lithosphere called the asthenosphere.

• There are three basic types of rock: Igneous, Sedimentary and Metamorphic.

Physical Features of the Earth

Major Concepts

Earth is segregated and concentrated into layers according to density.

• The major internal layers based on physical properties are:

(a) lithosphere (b) asthenosphere

(c) mesosphere (d) core

• Material within each of these units is in motion, making Earth a changing dynamic planet.

• Continents and ocean basins are the principal surface features of Earth.

Major Structural Units of Earth

• The constituents of Earth are separated and segregated into layers according to density.

• The denser materials - concentrated near the center, the less dense - near the surface.

• The internal layers are recognized on the basis of composition and physical properties which are:

• Crust

• Mantle – earth mass, which compose of composed of iron (Fe), magnesium (Mg),

aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. At over

1000 degrees C, the mantle is solid but can deform slowly in a plastic

manner.

• Core (inner & outer) - composed mostly of iron (Fe) and is so hot that

the outer core is molten, with about 10% sulphur (S).

The inner core is under such extreme pressure that

it remains solid.

• Layers based on physical properties are:

• Asthenosphere

• Lithosphere

• Mesosphere

• Core