THE BLUE

PLANET

EARTH

Why is earth often called the blue

planet?

The earth is often called blue planet

because it appears blue from space . It

is the only planet that contains water

in liquid form . In fact ,70% of earth’ s

sur face is water.

The layers of the earth

The earth mainly has four layers .

From the middle they are-

Crust

Mantle

Outer Core

Inner Core

Crust

The first layer consists of about 10 miles

(16km) of rock and loose materials

scientists call the crust. Underneath the

continents, the crust is almost three

times as thick as it is under the oceans.

Mantle

Travelling beyond the earths crust , we next

encounter the mantle . The mantle extends to a

depth of approximately 1,800 miles(2897 km)

andis made of a thick, solid ,rocky substance

that represents about 85% of the total weight

and mass of the earth.

Outer Core

Travelling still deeper within the earth ,

we next would encounter the outer core ,

which extends to a depth of around 3000

mile (4828 km)beneath the surface . It is

believed that the outer core is made up of

super – heated molten lava. The lavais

believed to be mostly of iron and nickel.

Inner Core

Finally, we would reach the Earth’s inner core. The inner

core extends another 900 miles (1448km) toward the center

of the Earth. It is believed that this inner core is a solid

ball of mostly iron and nickel.

Continents of the Earth

In the beginning all the continents were united . Pangaea or

Pangea was a supercontinent that existed during the late

Paleozoic and early Mesozoic eras. It assembled from earlier

continental units approximately 300 million years ago, and

it began to break apart about 175 million years ago. In

contrast to the present Earth and its distribution of

continental mass, much of Pangaea was in the southern

hemisphere and surrounded by a super ocean, Panthalassa .

Pangaea was the last supercontinent to have existed and

the first to be reconstructed by geologists.

Breaking of Pangea

The supercontinent , Pangea broke in seven

continents ,gradually and gradually. Those

seven continents from largest to smallest are –

Asia

Africa

North America

South America

Europe

Antarctica

Australia

AsiaAsia is the Earth's largest and most populous continent, located primarily in

the eastern and northern hemispheres. Asia covers an area of 44,579,000 square

kilometers, about 30% of Earth's total land area and 8.7% of the Earth's total

surface area. It has historically been home to the world's first modern

civilizations and has always hosted the bulk of the planet's human population

.Asia is notable for not only its overall large size and population, but unusually

dense and large settlements as well as vast barely populated regions within the

continent of 4.4 billion people. The boundaries of Asia are traditionally

determined as that of Eurasia, as there is no significant geographical

separation between Asia and Europe. The most commonly accepted boundaries

place Asia to the east of the Suez Canal, the Ural River, and the Ural

Mountains, and south of the Caucasus Mountains and the Caspian and Black

Seas. It is bounded on the east by the Pacific Ocean , on the south by the

Indian Ocean and on the north by the Arctic Ocean.

Africa

Africa is the world's second-largest and second-most-populous

continent. At about 30.2 million km2 (11.7 million square miles)

including adjacent islands, it covers six percent of Earth's total surface

area and 20.4 percent of its total land area .With 1.1 billion people as of

2013, it accounts for about 15% of the world's human population.The

continent is surrounded by the Mediterranean Sea to the north, both the

Suez Canal and the Red Sea along the Sinai Peninsula to the northeast,

the Indian Ocean to the southeast, and the Atlantic Ocean to the west.

The continent includes Madagascar and various archipelagos. It

contains 54 fully recognized sovereign states (countries), nine territories

and two de facto independent states with limited or no recognition .

North America

North America is a continent entirely within the Northern

Hemisphere and almost all within the Western Hemisphere. It

can also be considered a northern subcontinent of the Americas .

It is bordered to the north by the Arctic Ocean, to the east by

the Atlantic Ocean, to the west and south by the Pacific Ocean,

and to the southeast by South America and the Caribbean

Sea.North America covers an area of about 24,709,000 square

kilometers (9,540,000 square miles), about 16.5% of the earth's

land area and about 4.8% of its total surface. North America is

the third largest continent by area, following Asia and Africa

and the fourth by population after Asia, Africa, and Europe.

South AmericaSouth America is a continent located in the Western Hemisphere, mostly in the

Southern Hemisphere, with a relatively small portion in the Northern Hemisphere.

It is also considered as a subcontinent of the Americas which is the model used in

Spanish-speaking nations and most of South America.It is bordered on the west

by the Pacific Ocean and on the north and east by the Atlantic Ocean; North

America and the Caribbean Sea lie to the northwest. It includes twelve sovereign

states – Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Guyana, Paraguay,

Peru, Suriname, Uruguay, and Venezuela – and two non-sovereign areas –

French Guiana, an overseas department of France, and the Falkland Islands, a

British Overseas Territory . In addition to this, the ABC islands of the

Netherlands and Trinidad and Tobago may also be considered part of South

America. South America has an area of 17,840,000 square kilometers. Its

population as of 2005 has been estimated at more than 371,090,000. South

America ranks fourth in area and fifth in population . Brazil is by far the most

populous South American country, with more than half of the continent's

population, followed by Colombia, Argentina, Venezuela and Peru.

Europe

Europe is a continent that comprises the westernmost part of

Eurasia. Europe is bordered by the Arctic Ocean to the north, the

Atlantic Ocean to the west, and the Mediterranean Sea to the

south. To the east and southeast, Europe is generally considered as

separated from Asia by the watershed divides of the Ural and

Caucasus Mountains, the Ural River, the Caspian and Black Seas,

and the waterways of the Turkish Straits. Yet the borders of

Europe—a concept dating back to classical antiquity—are

arbitrary, as the primarily physiographic term "continent" also

incorporates cultural and political elements.

Antarctica

Antarctica is Earth's southernmost continent, containing the

geographic South Pole. It is situated in the Antarctic region of the

Southern Hemisphere, almost entirely south of the Antarctic Circle, and

is surrounded by the Southern Ocean. At 14,000,000 square kilometres

(5,400,000 square miles), it is the fifth-largest continent in area after

Asia, Africa, North America, and South America. For comparison,

Antarctica is nearly twice the size of Australia. About 98% of

Antarctica is covered by ice that averages 1.9 km (1.2 mi; 6,200 ft) in

thickness, which extends to all but the northernmost reaches of the

Antarctic Peninsula. Antarctica, on average, is the coldest, driest, and

windiest continent, and has the highest average elevation of all the

continents.

Australia

Australia is the smallest continent that lies entirely in the

Southern Hemisphere . It is surrounded by islands and seas on all

sides. Therefore it is also called Island Continent. Australia

comprises a land area of about 7.692 million square kilometres.

Although this is just five per cent of the world's land mass (149.45

million square kilometres), Australia is the planet's sixth largest

country after Russia, Canada, China, the United States of

America and Brazil. It is also the only one of the largest six

nations that is completely surrounded by water.

Movements of the Earth

The two main movements of the are –

Rotation - The movement of the earth

around its own axis is called rotation .

Revolution – The movement of the earth

on the elliptical path called orbit around

the sun is called revolution .

Rotation

The earth spins like a top. The movement of the

earth around its own axis is called rotation . The

earth takes 24 hours to complete one rotation. This

equals to a day and night . The side of the earth

which faces the sun has day and the opposite side

has night .

hfRevolution

The movement of the earth on the elliptical path called orbit

around the sun is called revolution .it takes 365 and one-

fourth days (one year) to revolve around the sun . We

consider a year as consisting of 365 days only and neglect

six hours for the sake of our convenience. Six hours saved

every year are added to make one day (24 hours) over a

span of four years . This surplus day is added to the month

of February. Thus, every fourth year , February is of 29

days instead of 28 days . Such a year with 366 days is

called leap year.

How are seasons formed ?

The cause of the formation of seasons is revolution of the earth

around the sun. The earth revolves around the sun in an elliptical

orbit. It completes its revolution in approximately 365 days. The

axis of the earth is tilted towards the plane of its orbit at an angle

of 23.5 degrees. The axis always points towards the same fixed

point in space: the polar star. Due to these arrangements seasons

are formed and the length of days and nights vary alternately.

Due to the inclination of the earth, the sun's rays fall on different

parts of the earth with varying intensity, making up for different

seasons in different hemispheres.

Domains of the Earth

The four major domains of the Earth are –

Lithosphere

Hydrosphere

Atmosphere

Biosphere

LithosphereEarth's lithosphere includes the crust and the uppermost mantle, which

constitute the hard and rigid outer layer of the Earth. The lithosphere is

subdivided into tectonic plates. The uppermost part of the lithosphere that

chemically reacts to the atmosphere, hydrosphere and biosphere through the

soil forming process is called the pedosphere. The lithosphere is underlain by

the asthenosphere which is the weaker, hotter, and deeper part of the upper

mantle. The boundary between the lithosphere and the underlying

asthenosphere is known as the Lithosphere-Asthenosphere boundary and is

defined by a difference in response to stress: the lithosphere remains rigid for

very long periods of geologic time in which it deforms elastically and through

brittle failure, while the asthenosphere deforms viscously and accommodates

strain through plastic deformation. The study of past and current formations

of landscapes is called geomorphology.

Hydrosphere

This includes water in liquid and frozen forms in groundwater, oceans, lakes and

streams. Glaciers, against popular belief, are part of the cryosphere and not part

of the Hydrosphere. Saltwater accounts for 97.5% of this amount. Fresh waters

accounts for only 2.5%. Of this fresh water 68.7% is in the "form of ice and

permanent snow cover in the Arctic, the Antarctic, and in the mountainous

regions. Next, 29.9% exists as fresh ground waters. Only 0.26% of the total

amount of fresh waters on planet Earth is easily accessible. It is found in lakes,

reservoirs and river systems, the principal elements of water ecosystems." The total

mass of the Earth's hydrosphere is about 1.4 × 1018 tonnes, which is about

0.023% of the Earth's total mass. About 20 × 1012 tonnes of this is in the earth’s

atmosphere (for practical purposes, 1 cubic metre of water weighs one tonne).

Approximately 75% of the Earth's surface, an area of some 361 million square

kilometers (139.5 million square miles), is covered by ocean. The average salinity of

the Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5%).

Atmosphere

The atmosphere of Earth is the layer of gases, commonly known as air, that

surrounds the planet Earth and is retained by Earth's gravity. The

atmosphere protects life on earth by absorbing ultraviolet solar radiation,

warming the surface through heat retention, and reducing temperature

extremes between day and night.By volume, dry air contains 78.09%

nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small

amounts of other gases. Air also contains a variable amount of water

vapour, on average around 1% at sea level, and 0.4% over the entire

atmosphere. Air content and atmospheric pressure vary at different layers,

and air suitable for use in photosynthesis by terrestrial plants and

breathing of terrestrial animals is found only in Earth's troposphere and in

artifical atmospheres.

BiosphereThe biosphere is the global sum of all ecosystems. It can also be termed as the

zone of life on Earth, a closed system (apart from solar and cosmic radiation

and heat from the interior of the Earth), and largely self-regulating . By the

most general biophysiological definition, the biosphere is the global

ecological system integrating all living beings and their relationships,

including their interaction with the elements of the lithosphere, geosphere,

hydrosphere, and atmosphere. The biosphere is postulated to have evolved,

beginning with a process of biopoesis (life created naturally from non-living

matter, such as simple organic compounds) or biogenesis (life created from

living matter), at least some 3.5 billion years ago. The earliest evidence for

life on Earth includes biogenic graphite found in 3.7 billion-year-old

metasedimentary rocks from Western Greenland and microbial mat fossils

found in 3.48 billion-year-old sandstone from Western Australia. More

recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old

rocks in Western Australia. According to one of the researchers, "If life arose

relatively quickly on Earth ... then it could be common in the universe."

Global Warming

It occurs due to increase of carbon dioxide

in the atmosphere. As , carbon dioxide

traps heat and does not let it go in the

space. If , there will be more of carbon

dioxide more heat will be trapped and thus,

it will lead to increase in temperature of

the earth. This whole process is called

global warming .