Long ago, people used to think the
Earth was flat. They believed if they sailed a boat far out into the ocean, the
boat would fall off the Earth! Now people know that this is not true. We know
the Earth is not flat. It is shaped like a ball. The Earth only looks flat to
us because it is so large. We can only see a small part of the Earth's surface
when we are standing on it.
Inside the earth
The interior structure of the Earth is layered in spherical shells, like
an onion. According to scientific studies, the earth from the top to center can
be divided into three parts: Crust, Mantle
and the Core. Core further subdivided into
outer core and inner core.
Earth has an outer silicate solid crust, a highly viscous
mantle, a liquid outer core that is much less viscous than the mantle, and a
solid inner core. The outer skin of the earth is called crust. The crust of the
Earth is like the skin of a peach. The skin on the peach is very thin. It is
only a small part of the peach. The crust of the Earth is also very thin. It is
only a small part of the Earth. The crust is the Earth's thinnest layer. The
crust is composed mainly of basalt and granite and, with the uppermost part of
the upper mantle, is broken into tectonic plates. The crust is cooler and more
rigid than the deeper layers. The thickness of the crust varies
considerably. The thickness of the
crust varies from 5 to 10 km
under the oceans and continents the crust is made up of three kinds of rocks
- igneous sedimentary and metamorphic
.Beneath the earth’s crust are the mantle, the earth’s the
mantle is a thick layer of solid
rocks and goes down to about 2900 km. The rocks in the mantle are made up of silicon,
oxygen, aluminum, iron and magnesium its temperature increases from 870c
to2200c as we go down. The outer core is about 2200 km thick and is made of
melted iron and nickel. Its temperature ranges from 2200 C(upper most part) to
5000 C (deepest part). The ball shaped inner core is about 5150 km below the earth’s
surface. The centre of the inner core is about 1200km below the inner boundary
of outer core. It is made of solid iron and nickel.
The
large zone corresponding to the flesh of the peach is called the
"mantle." It is made mostly of rocky minerals with names like
olivine, pyroxene, quartz, and periclase. (Any good book on geology or
mineralogy will tell you everything you ever wanted to know about these
minerals.) Almost all rocks are made of silicon and oxygen mixed with other
elements, such as calcium, aluminum, and iron. Mantle rock contains
particularly large amounts of iron and magnesium. The mantle is also divided
into two solid parts, the lower mantle and the upper mantle. This division in
the mantle may be due to small differences in the amounts of iron and magnesium
or to differences in the nearness of atoms to each other. (As an analog, think
of a piece of Styrofoam.
Atmosphere
The
earth is surrounded by the atmosphere, which is the body of air or gasses that
protects the planet and enables life. Most of our atmosphere is located close
to the earth's surface where it is most dense. The air of our planet is 79%
nitrogen and just under 21% oxygen; the small amount remaining is composed of
carbon dioxide and other gasses. There are five distinct layers of the earth.
Let's look at each, from closest to farthest from the earth.
The
layer of the atmosphere closest to the earth is the troposphere. This layer is
where weather occurs. It begins at the surface of the earth and extends out to
about 4-12 miles. The temperature of the troposphere decreases with height.
This layer is known as the lower atmosphere.
The envelope of
air which surrounds the earth from all sides is called atmosphere is held due
to the gravitational pull of the earth. The Earth's atmosphere is more than
just the air we breathe. It's also a buffer that keeps us from being peppered
by meteorites, a screen against deadly radiation, and the reason radio waves
can be bounced for long distances around the planet. The outer layer of the atmosphere is called
exosphere which extended up to an altitude of 2000km above the sea level.
All gases of the
atmosphere combined together constitute air. Atmosphere contains 78%nitrogen, 21%
oxygen and remaining 1 % consists of argon, carbon dioxide, neon, helium, ozone
and hydrogen. Air also contains water vapor and particles of dust. In the lower layer of the atmosphere, the ratio
of different gases remains relatively constant but the percentage of water vapor
goes on changing. Clouds float in the lowest part of the atmosphere called troposphere.
The air gets thinner, as we go above the surface of the earth. The lowest is
the troposphere, which is the layer that provides most of our weather. It
contains about four-fifths of the Earth's air, but extends only to a height of
about 11 miles (17 kilometers) at the Equator and somewhat less at the Poles. The
name comes from a Greek word that refers to mixing. And mixing is exactly what
happens within the troposphere, as warm air rises to form clouds, rain falls,
and winds stir the lands below. Typically, the higher you go in the troposphere,
the colder it gets. Above the troposphere is the stratosphere. It extends to a
height of about 30 miles (50 kilometers) and includes the ozone layer, which
blocks much of the sun's harmful ultraviolet rays. The stratosphere is warmer
than the troposphere because of the energy from the ultraviolet light absorbed
by the ozone. At its base, the stratosphere is extremely cold, about -110
degrees Fahrenheit (-80 degrees Celsius). At its top, the temperature has risen
back nearly to freezing. Next comes the mesosphere. In this layer, the air
temperature drops again, down to nearly -180 degrees Fahrenheit (-120 degrees
Celsius) at the top. Meteors generally burn up in the mesosphere, which extends
to a height of about 52 miles (85 kilometers). This is why the Earth's surface
isn't pocked with meteor craters, like the moons.
