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Astronomy - Planet Earth
Mass: 5.976 X 1024 kg (1 Earth)
Radius (equatorial): 6378 km
Mean density: 5.515 g cm-3
Distance from Sun: 149 600 000 km
Rotational period: 0.99727 days
Orbital period: 365.256 days
Escape velocity: 11.18 km s-1
Surface temperature: 15°C (mean)
Atmospheric composition: nitrogen (77%), oxygen (21%),
other (2%)
Characteristics
Our planet Earth is the only planet known to harbor life. There are many
intertwining factors why life thrives on the Earth both in terms of quantity and
variety. Being the third planet, it is situated at a mean distance of just short of
150 000 000 km from the Sun, a distance that is neither too cold nor too hot for
water to exist, an essential ingredient for living organisms. Earth's thick
atmosphere helps to regulate the temperature that prevent excessive heat from
baking the surface while burns most meteorites before they hit the Earth. At night
the Earth's molten nickel-iron core warms the surface and prevents excessive
cooling. The molten core also generates strong magnetosphere and, together with
the atmosphere, shield the Earth from nearly all harmful radiation coming from
the Sun (and other stars).
The Earth's atmosphere consists of 77% nitrogen and 21% oxygen. The former is
chemically inert that helps to stabilize the atmosphere. Without it, the chemically
reactive oxygen will react with many materials, leading to spontaneous
combustion. In addition, the tiny amount of carbon dioxide (~0.03%) is acting as
a moderate green house agent. The gas retains heat so that the average surface
temperature is maintained at a comfortable 15°C. Otherwise, the temperature will
easily drop to around -20°C and ocean would freeze.
Geologically speaking, the Earth's surface is very young, about 500 000 000
years. Erosion and tectonic processes destroy most of the traces of earlier
geologic surface history. Nowadays, it is very difficult to find rocks older than 3
billion years old, about 1.5 billion years short of the Earth's age. About 71% of
the Earth surface is covered with water. Earth is the only planet where water can
exist in liquid form. The presence of large amount of water also helps to regulate
the temperature. The liquid water is also responsible for a variety of geochemical
processes such as erosion, migration and cyclization of minerals and elements.
Oxygen accounts for about 47% of Earth's crust by weight,
while silicon and aluminium comprise of 27% and 8% respectively. Complex
cyclization processes (carbon cycle, nitrogen cycle etc) between atmosphere and
surface ensure supplies of biologically important elements are properly
maintained, often involving waters as intermediaries.
Earth has only one satellite, the Moon. Interesting gravitational effects between
the Earth and Moon result in the tides. The gravitational interaction also causes
the Moon to rotate synchronously, that is, it is locked in phase with its orbit so
that the same side is always facing the Earth. In addition, Earth is known to have
'companions' which have complicated orbital relationship with the Earth. One
example is the Asteroid 3753 Cruithne.
6. The Earth’s magnetic field protects it
Earth has a magnetic field with magnetic poles close to the North and South geographic poles. This
magnetic field is so strong that its influence reaches thousands of kilometers from the surface of the Earth
to the magnetosphere. The magnetosphere is one of the reasons why life can exist on Earth. It acts as a
kind of shield, diverting harmful radiation from the Sun away from the Earth where it would severely
damage, if not destroy, life. Scientists theorize that the currents of the Earth’s liquid outer core cause this
magnetic field.