Earth...Among the vastness of the universe ,hidden within a
beautiful spiral galaxy ,orbiting one of its many billions of
stars.there exixts a very special place.it is a planet that may be
the only one of its kind in all of the universe.it is a place
called Earth.A world of vast oceans and stromy seas.A world of
magnificent clouds and life giving rain.it is a world of towering
mountains and frigid ice.it is a world of forested hills and
dessert sands .Most of all,it is a world of spectacular
beauty.Earth began as a child of the sun almost 5 billion years
ago.it was voilent birth.and a difficult childhood but slowly earth
grew up.and somewhere in its ancient saes life was born.it was the
dawn of a new world and new science to study itintroduction of
earthEarth is the 3rd planet from the Sun at a distance of about
150 million kilometers (93.2 million miles). It takes 365.256 days
for the Earth to travel around the Sun and 23.9345 hours for the
Earth rotate a complete revolution. It has a diameter of 12,756
kilometers (7,973 miles), only a few hundred kilometers larger than
that of Venus. Our atmosphere is composed of 78 percent nitrogen,
21 percent oxygen and 1 percent other constituents.Earth is the
only planet in the solar system known to harbor life. Our planet's
rapid spin and molten nickel-iron core give rise to an extensive
magnetic field, which, along with the atmosphere, shields us from
nearly all of the harmful radiation coming from the Sun and other
stars. Earth's atmosphere protects us from meteors, most of which
burn up before they can strike the surface.
Earh is a old english word for land.it belong to galaxy local
group.cluster virgo and super cluster.it is the only planet to
sustain life.some effect about the earthsun is not move.other
planet are movingit is the third planet and fifth largest
planet.its distance from the sun is 149600000 km.its mass is 5.972
* 1024 kg.History.People thing that earth is flat but Aristotle
give theory that earth is spherical.the diameter of earth at pole
12715 km(minor axis) at equator its diameter is 12763 km(major
axis).structure of earth surfaceit divided into four layers....1)
crust 2) mantle 3) inner core 4) outer core
1) crustit is outer part of earth.There are two different types
of crust: thin oceanic crust that underlies the ocean basins and
thicker continental crust that underlies the continents. These two
different types of crust are made up of different types of rock.
The thin oceanic crust is composed of primarily of basalt and the
thicker continental crust is composed primarily of granite. The low
density of the thick continental crust allows it to "float" in high
relief on the much higher density mantle below.also called SIMA
layer and SIAL layer.2) MantleEarth's mantle is thought to be
composed mainly of olivine-rich rock. It has different temperatures
at different depths. The temperature is lowest immediately beneath
the crust and increases with depth. The highest temperatures occur
where the mantle material is in contact with the heat-producing
core. This steady increase of temperature with depth is known as
the geothermal gradient. The geothermal gradient is responsible for
different rock behaviors and the different rock behaviors are used
to divide the mantle into two different zones. Rocks in the upper
mantle are cool and brittle, while rocks in the lower mantle are
hot and soft (but not molten). Rocks in the upper mantle are
brittle enough to break under stress and produce earthquakes.
However, rocks in the lower mantle are soft and flow when subjected
to forces instead of breaking. The lower limit of brittle behavior
is the boundary between the upper and lower mantle.3)outer
coreEarth's Core is thought to be composed mainly of an iron and
nickel alloy. This composition is assumed based upon calculations
of its density and upon the fact that many meteorites are
iron-nickel alloys. The outer core is a liquid because the
temperatures there are adequate to melt the iron-nickel alloy. also
called NIFI layer.it laso contain lighter element such as Si,S,C or
O.its ranges is 2900 km to 5150 km and 2300 km thick.
4) Inner coreit is fourth layer and composed by solid Iron. the
inner core is a solid even though its temperature is higher than
the outer core. Here, tremendous pressure, produced by the weight
of the overlying rocks is strong enough to crowd the atoms tightly
together and prevents the liquid state.its thickness is 5150 to
6370 km.
