Earth is one of the planets of our solar system and it belongs to Milky way galaxy.
It has only one natural satellite called the moon.It is the third planet from the sun.Its weight is roughly
5,974,000,000,000,000,000,000,000 kilograms. According to our knowledge it is the only planet that has life.
It has 70% water.Once upon a time people believed that earth is flat in shape. The earth rotates west to east on
its axis. Orbital period of the earth is 23 hours, 56 minutes, and 4 seconds. It takes 365.24 days to rotate around
the sun. Ozone layer is found in the stratosphere. Ozone layer saves us from the ultraviolet radiation coming from
the sun. In ancient times people believed that earth is the center of the universe. Polish astronomer Nicolaus
Copernicus put forth that sun is the center of the universe and all planets are revolving around the sun. Earth’s
atmosphere is divided into five main layers. They are troposphere, stratosphere, Mesosphere, thermosphere and
Troposphere : 0 km to 12 km. (0 to 7 miles)
Stratosphere : 12 km to 50 km. (7 to 31 miles)
Mesosphere : 50 km to 80 km. (31 to 50 miles)
Thermosphere : 80 km to 700 km. (50 to 440 miles)
Exosphere : 700 km to 10,000 km. (440 to 6,200 miles)
Composition of air
Nitrogen 78 percent
oxygen 21 percent
Argon 0.6. percent
Carbon dioxide 0.04 percent
There are some other gases in trace amount. They are helium, neon, methane, krypton, hydrogen
and water vapour.
The inner parts of earth divided into four layers. They are crust, mantle, outer core and inner core.
The outermost solid part is crust. It is divided into oceanic crust and continental crust. The Crust
thickness averages about 30 kilometers (18 miles) under the continents, but only about 5
kilometers (3 miles) under the oceans. The thickness of Earth’s mantle is 2,900 km thick.
The composition of Earth’s mantle is molten/solid rock. The thickness of outer core is 2,300 km
(1400 miles). It is composed of nickel-iron alloy. Inner core is earth’s inner most
part. The Inner Core is about 1250 km thick and is the second smallest layer. At
the very center of the earth, the gravitational force is zero.