THE EARTH | GEOGRAPHY

THE EARTH

THE EARTH
THE EARTH

Only planet of our Solar System where life exists.
Also called “Blue Planet“.
Circumference 40008 km (polar) and Equatorial circumference 40075 km.
Area Nearly 510 million sq. km.
5th largest planet of our solar system.
Perigee Nearest position of the Earth to the Moon (356000 km).
Apogee Farthest position of the Earth from the Moon (407000 km).
Apihelion Farthest position of the Earth from the Sun on July 4,about 152 million km.
Perihelion Nearest position of the Earth to the Sun on January 3,about 147 million km.
Its 70% part is filled up of water.
Shape is Oblate Ellipsoid or Oblate Spheroid.
It is third planet of our solar system.
It takes 24 hr to complete one rotation.

COMPOSITION OF THE EARTH

Made up of over 100 elements.

The following 8 elements are important.

Oxygen
46.5%
Silicon
27.72%
Aluminium
8.13%
Iron
5.01%
Calcium
3.63%
Sodium
2.85%
Potassium
2.62%
Magnesium
2.09%

EARTH MOVEMENTS

ROTATION

Earth rotates Westward to Eastward (anti-clockwise) in 23 hrs 56 min and 40.91 sec.
Due to this rotation days and night are occurred there and also there is a change in the direction of wind and ocean currents.
Rotation velocity at equator is 1667 km/hr and at poles it is zero.
Axis is an imaginary line passing through the centre on the Earth and running from North to South at an angle of 66.50 to the plane of the Earth’s orbit.
The longest day in North Hemisphere is 21 June (summer solstice) while shortest day is on 22 December (winter solstice) vice-versa in South Hemisphere.
Days and nights are equal at the equator.

REVOLUTION

Earth takes 365 days,5 hr,48 min and 45.51 sec to complete a revolution.
Due to the revolution there is a change in season and also due to tilt of the Earth’s axis at 66.5.

THE FOUR SEASONS

Spring March 21, this is the season of Spring in the North Temperate Zone.The Sun is directly overhead the equator (vernal equinox).
Summer June 21,The North Temperate Zone experiences summer because the Sun is directly overhead the Tropic of Cancer (summer solstice).
Autumn September 23,The North Temperate Zone experiences autumn because the Sun returns to the equator (autumnal equinox).
Winter December 22,The North Temperate Zone experiences winter.The Sun is at the Capricorn (winter solstice).

INTERNAL STRUCTURE OF THE EARTH

INTERNAL STRUCTURE OF THE EARTH
INTERNAL STRUCTURE OF THE EARTH

THE EARTH’S CRUST

The outermost solid cover or shell of the Earth is known as the Earth’s crust.
The thickness of the crust is about 30 km.
The density of the rocks in the Earth’s Crust ranges from 2.7 to 3 g/cc (grams per cubic centimeter).
The upper part of the crust consists of silica and aluminium in greater proportions.That is why,it is called “Sial”.
Where is the lower part of the crust is called “Sima” because the proportion of silica and magnesium is higher in this part.

MANTLE

This layer lies below the crust.
Its thickness is about 2900 km and the density of substances in the mantle ranges from 3.0 to 4.7.

CORE

The Earth’s core lies below the mantle.Its thickness may be about 3471 km.
Its radius is 6371 km.
It is divided into two parts the outer core and inner core.The outer core is probably in a liquid state and the inner core in a solid state.
The core mainly consists of iron with some amount of nickel and sulphur .
After the mantle the earth’s density goes on increasing rapidly towards its centre and finally is more than 13.
The temperature of the central part of the Earth may be about 5000C.
Discontinuities within Earth layers.
Mohorvic discontinuity-Between lower crust and upper mantle.
Gutenburg discontinuity -Between mantle and core.

LONGITUDE 

It’s an Imaginary line Measured in degrees West to East of Greenwich from 00 to 1800 meridian.
It is the angular distance measured from the centre of the Earth.

At equator
10=111 km.
300 N or 300 S =96.5 km goes on decreasing  this way until it is zero at the poles.
Longitudes have very important functions to help in determining local time in relation to Greenwich Mean Time (GMT).

ANTIPODAL POINTS

180 meridian (International Date Line ) lies exactly opposite to 00 meridian. Such points are known as Antipodal Points.
Earth is divided into 24 longitudinal zone.
4 min =10,1 hr =150

LATITUDE 

It is the angular distance of a point on the Earth’s surface, measured in degrees from the centre of the Earth.
Latitude lines drawn parallel to the equator.
One degree latitude =111 km (Approx).
Each degree is subdivided into 60 min and each min into 60 sec.

The equator represent 00 latitude.
North Pole =900 N
South Pole =900 S
Tropic of Cancer =23.50 N
Tropic of Capricorn =23.50 S
Arctic Circle =66.50 N
Antarctic  Circle =66.50S

STANDARD TIME AND TIME ZONES

Most countries adopt their standard from the central Greenwich mean time.
The whole world has been divided into 24 standard time zones.
Each zone, therefore, is separated by 150 longitudes or by one hour thus,150=1 hour.
Larger countries like USA, Canada, Russia, having greater East-west stretch have to adopt several time zone.
Russia has 11 time zone.
India has only one time zone. The Indian Government has accepted the meridian of 82.50 East (near Allahabad ) for the standard time which  is 5 hr 30 min ahead of Greenwich Mean Time.

GREENWICH MERIDIAN

Marks the starting points of every time zone in the world.
GMT is World Time and the basis of every world time zones, which sets the time of day and is at the centre of the time zone map.
Greenwich defines both time and place for the whole world.
Greenwich, England, Longitude 000’0”, latitude 51028’38” N (North of equator) has been the home of Greenwich Mean Time (GMT) since 1884.

INTERNATIONAL DATE LINE 

It is the 1800 meridian running over the Pacific Ocean deviating at Fiji, Soma and Gilbe  Islands.
This meridian is considered to be deviated at the land masses so that the travelers do not feel inconvenient.
One who crossing the Date Line from West to East repeat a day and travelers crossing it from East to West lose a day.

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