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Earth 169-
A LARGE BALL OF ROCK spinning through space is our home in
the universe. This is Earth, one of the eight major planets that circle
around the sun. Earth is the only place we know of that supports life. It
has liquid water and a protective atmosphere, both of which are essential
for life. And of all the planets in the solar system, Earth is at just the right
distance from the sun to be neither too hot nor too cold. Land makes
up less than one-third of the surface of Earth; more than two-thirds is
the water in the oceans. Earth’s interior consists of layers of rock that
surround a core made of iron and nickel.
The processes that support life on Earth are in a natural balance.
However, many people are worried that pollution, human
overpopulation, and misuse of resources may destroy
this balance and make Earth unsafe for
plants and animals.
ATMOSPHERE
A layer of air called the atmosphere surrounds Earth.
It is roughly 1,250 miles (2,000 km) deep and contains
mainly the gases nitrogen and oxygen. The atmosphere
shields Earth from harmful ultraviolet rays coming
from the sun and prevents Earth from becoming
too hot or too cold.EARTH IN SPACE
When astronauts first saw Earth
from space, they were enthralled
by the beauty of our blue planet.
This picture shows Earth over
the moon’s horizon.
OCEANS
The oceans are large water-filled
hollows in Earth’s crust. Their
average depth is 2.2 miles (3.5 km).
MANTLE
Under the crust is the mantle,
a layer of rock about 1,800 miles
(2,900 km) thick. The temperature
rises to 6,700°F (3,700°C) at the
base of the mantle, but high
pressure there keeps the rock solid.OUTER CORE
The core of Earth consists of two
layers—the outer core and the
inner core. The outer core is about
1,240 miles (2,000 km) thick and
is made of liquid iron. Its
temperature is approximately
4,000°F (2,200°C).INNER CORE
A ball of solid iron and
nickel with a radius of
about 1,712 miles (2,740 km)
lies at the center of Earth. The
temperature at the center is
about 8,100°F (4,500°C).
Inner coreOuter coreEarth is
made of
layers of
air, water,
iron, nickel,
and rock
around a core
of iron and nickel.Mantle LIQUID ROCK
The interior of
Earth is very
hot, heated by
radioactive decay
of the rocks
inside Earth.
The temperature
is so high that
some rock inside
Earth is molten.
This liquid rock
rises to the
surface at
volcanoes, where
it is called lava.CRUST
The top layer of rock at the surface
of Earth is called the crust. It is up
to 44 miles (70 km) deep beneath
the continents, but as little as 4 miles
(6 km) deep under the oceans. The
temperature at the bottom of the
crust is about 1,900°F (1,050°C).AtmosphereClouds containing tiny
drops of water float low in
the atmosphere, carrying
water from the seas and
land that falls as rain.Crust