about the blue planet, earth
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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 .
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