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Earth
Facts
Earth is
the third planet, and 93,000,000 miles (150,000,000
km.) from the sun. It is estimated to be over 4.5
billion years old.
The planet
rotates once every 23 hours, 56 minutes, and 4.09
seconds. It makes one full revolution around the
sun every 365 days, 6 hours, 9 minutes, and 9.45
seconds. Earth's axis is tilted at a 23.5°
angle.
Earth has a total surface
area of 196,800,000 square miles. Approximately 57,300,000 square
miles, or 29% of the total surface area is land. Water covers
approximately 139,500,000 square miles, or 71% of the total surface
area.
The highest
temperatures on Earth have reached 136° F
(58° C) at Al Asisiyah, Libya. Temperatures of
- 128° F (-89° C) have been recorded at
Vostok station in Antarctica.
The
atmosphere is a thin, gaseous layer of air that
envelops the planet. Its inner layer is called the
troposphere and reaches only 11 miles above sea
level. It contains most of the planet's air, which
consists of nitrogen (78%) and oxygen (21%). The
stratosphere, or outer layer, stretches 11-30 miles
above sea level and contains ozone (O3). Ozone
filters out most of the sun's harmful ultraviolet
radiation.
More than
99% of earth's atmosphere is less than 50 miles (80
km.) high. However, particles of the atmosphere are
found 1,000 miles (1,600 km.) in space above the
planet's surface.
Our
Sun
Our sun is
the source of energy for life. Solar energy drives
the climate and weather systems of our planet. The
sun is a huge ball of hydrogen (72%) and helium
(28%) gases. Tremendous pressure and temperatures
in its inner core fuses the hydrogen nuclei and
forms helium, releasing enormous amounts of energy.
This energy
travels at the speed of light and reaches Earth in
slightly more than 8 minutes. Earth receives only
about one-billionth of the sun's energy. About 34%
of the solar energy reaching the troposphere is
reflected back into space by clouds, dust,
chemicals. Most of the energy reaches the
troposphere as visible light, infrared radiation,
and a small amount of ultraviolet radiation that
wasn't absorbed by the stratosphere.
This
unreflected solar radiation is turned into infrared
radiation, or heat. Heat-trapping gasses like water
vapor, carbon dioxide, methane, nitrous oxide, and
ozone affect the speed at which this radiation is
returned to space. Without these gasses, known as
the natural greenhouse effect, heat would
immediately return to space, making it almost as
cold as Mars.
Forming
Life on Earth
Scientists
have studied fossils and made chemical analysis of
rocks to find out how life on Earth evolved to its
present system. Several theories have been
suggested. It is theorized by some scientists that
life developed in two phases over billions of
years.
In the
first phase explosions of dying stars shattered
through our galaxy and created swirling clouds of
dust particles and hot gases. These extended
trillions of miles across space. As the cloud
cooled, bits of matter began to cling to each
other. Over 4 billion years ago the cloud had
formed into a flattened, slowly rotating disk. Our
sun was born in the center of this disk. Farther
out on the disk, Earth and the other planets formed
as bits of matter were drawn together. Earth
started out as a molten mass that did not cool for
millions of years. As it cooled it formed a thin,
hard crust with no atmosphere or oceans.
Molten rock
frequently erupted through the crust. Water vapor
was released from the breakdown of rocks during
volcanic eruptions. Eventually the crust cooled
enough for this vapor to condense and come down as
rain to form the oceans that covered most of
Earth.
In the
second phase scientists have recently hypothesized
that bubbles floating on the ancient ocean trapped
carbon-containing molecules and the other chemicals
necessary for life. These bubbles may have popped
and released these chemicals into the atmosphere.
Organic compounds formed and dissolved in the early
atmosphere, collecting in the shallow waters of the
earth. Although no one knows how, the first living
cells developed between 3.6 and 3.8 billion years
ago. Over time these protocells developed into
cells having the properties we describe as life.
These
single-celled bacteria multiplied in the warm,
shallow waters for billions of years. Here they
mutated and developed into a variety of protists,
fungi and, about 600 million years ago, plants and
animals.
Life could
not develop on land since there was no ozone layer
to shield early life from damaging ultraviolet
radiation. Then about 2.3-2.5 billion years ago
photosynthetic bacteria emerged. These cells could
remove carbon dioxide (CO2) from the atmosphere
and, using sunlight, combine it with water to make
carbohydrates. In the process they created oxygen
(O2) and released it into the ocean. Some of the
oxygen escaped into the atmosphere.
Our
atmosphere was created over a span of 2 billion
years. Some of the oxygen was converted into ozone
(O3), which formed in the lower stratosphere and
protected life forms from UV radiation. This
allowed green plants to live closer to the surface
of the ocean, making it easier for oxygen to escape
into the atmosphere. About 400-500 million years ago the
first plants began to exist on land. Over the
following millions of years a variety of land
plants and animals evolved.
Living
Earth
Earth is
truly a remarkable planet. It is the only planet in
our solar system that has the components necessary
to support life as we recognize it. The planet is
only a tiny part of the universe, but it is the
home of human beings and many other organisms.
Animals and plants live almost everywhere on the
surface of Earth.
These
organisms can live on Earth because it has an
atmosphere. The atmosphere moderates daytime and
nighttime temperature swings. The atmosphere
filters radiant energy during the day, preventing
the surface from overheating. At night the
atmosphere prevents most of the radiant heat from
escaping back into space, keeping the surface
warm.
Most
organisms - both plants and animals - must also
have water to live. Earth has plenty. Seventy-one
percent of its surface is covered by water.
Living
things also need nitrogen, oxygen, and carbon
dioxide. Earth's thin layer of atmosphere provides
all of these elements.
The
atmosphere also screens out lethal levels of the
sun's ultraviolet radiation. The atmosphere,
however, could not exist if Earth were not at the
exact distance it is from the sun.
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