2. An Introduction to Earth
Earth, the planet on which we live
was formed about 4.5 billion years
ago. It is fifth largest in the solar
system and first largest in the inner
planets of the solar system. It has the
3rd position from the sun and 6th
position from outer planets. It is
known as the unique planet because it
is the only planet in the universe
which is known to have life.
3. It’s surface has water, land and is surrounded by a blanket of air
known as Atmosphere. These things help in the possibility of life. It’s
position from the sun also help in possibility of life because if it is too
near the sun, so it will be having very hot temperature and if it is too
far from the sun, so it will be having very cold temperature. When
astronauts first saw the earth from the space, it looked blue in color
because of the presence of water all over the surface. So, astronauts
named the earth ‘Blue Planet’ or ‘Watery Planet’. It is also known as
‘Terra’. It is the only in the solar system which is not named after a
4. Motions of the Earth
The Earth is having two types of motions:-
Earth has an imaginary line on which it rotates,
known as Axis. Earth’s orbit is slanting which
makes unequal days and nights on earth. When
the earth rotates on its axis, it is called Rotation.
Rotation causes days and nights on earth. Earth
takes 24 hours to complete one rotation. Earth
takes rotation from west to east. Earth has the
speed of 30 km of rotation on equator while on
poles it has 0 km. Earth completes one rotation
in 23 hours, 56 minutes and 4.1 seconds.
Earth has an imaginary line on which it
goes around the sun, known as Orbit.
Earth’s orbit is oval which brings the earth
near the sun and far from the sun. when the
earth goes around the sun, it is called
Revolution. Revolution causes changes in
the seasons on the earth. Earth takes 365
days, 5 hours, 48 minutes and 56 seconds
(3651/4 days) to complete one revolution.
Revolution also runs from west to east.
7. Difference between Rotation & Revolution
• The movement of the earth on it’s
axis is called Rotation.
• Rotation causes days and nights.
• Rotation is done in 23 hours, 56
minutes and 4.1 seconds.
• The movement of the earth around
the sun is called Revolution.
• Revolution causes seasons.
• Revolution is done in 365 days, 5
hours, 48 minutes and 56 seconds.
8. Layers of the Earth
Earth has three types of layers, they are:-
The crust ranges from 5–70 km (3–44
miles) in depth and is the outermost layer.
The crust is of two types:-
10. The thin parts are the oceanic crust, which underlie the ocean basins
(5–10 km) and are composed of dense (mafic) iron magnesium silicate
igneous rocks, like basalt. The thicker crust is continental crust, which
is less dense and composed of (felsic) sodium potassium aluminums
silicate rocks, like granite. The temperature of the Earth crust range
from 500 Â°C (900 Â°F) to 1,000 Â°C (1,800 Â°F). Temperature
generally increases with an increase in depth and the average
temperature of Earth.
The Mantle is the between layer of the earth and the thickest layer of
the earth. Earth's mantle extends to a depth of 2,890 km. The mantle
is composed of silicate rocks that are rich in iron and magnesium
relative to the overlying crust. The temperature of the mantle is 3,700
degrees Celsius. Convection of the mantle is expressed at the surface
through the motions of tectonic plates.
Core is the innermost layer of the earth. The core is of two types:-
13. Inner Core
The inner core of the Earth, its innermost part, is a primarily solid
ball with a radius of about 1,220 km (760 mi), according to
seismological studies. This is about 70% of the length of the Moon's
radius. It is believed to consist primarily of an iron–nickel alloy, and
to be about the same temperature as the surface of the Sun:
approximately 5700 K (5430 °C). The Earth was discovered to have a
solid inner core distinct from its liquid outer core in 1936, by the
seismologist Inge Lehmann Based on the relative prevalence of
various chemical elements in our solar system, the theory of planetary
formation, and constraints imposed or implied by the chemistry of the
rest of the Earth's volume, the inner core is believed to consist
primarily of a nickel-iron alloy known as NiFe. 13
14. Outer Core
The outer core of the Earth is a liquid layer about 2,266 km (1,408 mi)
thick composed of iron and nickel which lies above the Earth's solid
inner core and below its mantle. Its outer boundary lies 2,890 km
(1,800 mi) beneath the Earth's surface. The transition between the
inner core and outer core is located approximately 5,150 km (3,200
mi) beneath the Earth's surface. The temperature of the outer core
ranges from 4400 °C (8000 °F) in the outer regions to 6100 °C (11000
°F) near the inner core. Without the outer core, life on Earth would be
very different. Convection of liquid metals in the outer core creates the
Earth's magnetic field.
15. The Story of Earth
As you know, the earth was formed about 4.6 billion years ago, it’s
story starts. The Earth will live 4.5 million years more. If you want to
watch the story of the earth, here’s a hyperlink.
D:VideosThe Story of Earth.mp4