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Planet Earth
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Earth, the third planet from the Sun, takes 365 days to complete 1 orbit.
Earth's overall structure consists of:
 a dense, metallic, two-zone (solid inner, liquid outer) core
 a less dense, rocky mantle
 a thin (10-50 km) rocky crust containing the continents and ocean floor
 a gaseous, nitrogen + oxygen atmosphere
 a liquid H2O ocean, covering 75% of the surface
 a global magnetic field
The Earth's interior is NOT uniform in density, temperature or composition. These
properties change from the center to the surface of the planet.
Earth's interior structure originated early in its history, when the planet was largely
molten.
Earth possesses a thin atmosphere, with most of the mass lying within 10 kilometers of
the surface.
The atmosphere is largely transparent to visible radiation, and is put into motion via the
effects of solar heating on the land and ocean surfaces.
Earth's abundant atmospheric oxygen is unique within the solar system and is a direct
consequence of living organisms. The composition of the current atmosphere is
completely different from Earth’s original atmosphere.
Earth's global magnetic field produces the magnetosphere, a region completely
surrounding Earth, thousands of miles from the surface.
The magnetosphere shields the Earth from the solar wind and funnels charged atomic
particles towards the polar regions, producing aurora (also known as the Northern
Lights).
Earth's crust is dynamic – the continents drift across the surface; fresh material is
brought to the surface via volcanoes; earthquakes occur frequently; wind, water and
ice sculpt the surface.
Due to Earth’s active geology, the shape and location of land masses has changed
with time, over Earth’s 4.5 billion year history.
Tides are produced on Earth due to its unique property of having 75% of its surface
covered with a liquid. The tides result from the differential gravitational force
exerted on the Earth by the Moon and the Sun.
Earth formed from matter which condensed from the solar nebula. Heat from the Sun
prevented the abundant light elements hydrogen and helium from remaining
gravitationally bound to the proto-Earth.