Earth

Earth
Description
Adjectives:	Tellurian
Distance from Sun:	149.6 million km
Diameter:	12,742 km
Radius:	6,371 km
Temperature:	331 K to 183 K
Known Moons	1

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago.

It is the largest of the four terrestrial planets, measuring nearly 13,000 km in diameter.

Information

Earth is the only planet known to support life in the Solar System. Because of it's mild temperature and amount of water, it is a near-perfect planet for life to exist. About 71% of Earth's surface is covered by water, including oceans, lakes and rivers, although only 2.5% of it is freshwater. 

Life on Earth is predicted to have begun within the first billion years of its creation, although life on dry land would have begun at around 400 million years ago. The tallest mountain on earth is Mount Everest, however it is about one third of the size of Olympus Mons, the tallest point on Mars.

Moon

Main article: Moon

The Moon is a relatively large natural satellite compared to other moons in the Solar System. With a diameter about one-quarter of Earth's, the moon is a terrestrial planet-like satellite. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger in relative to the dwarf planet, Pluto.

Atmosphere and gravity

Earth's atmosphere is composed mainly of nitrogen, oxygen, argon and carbon dioxide. With nearly 80% of the atmosphere composed of nitrogen, several other gases are present including gases of which only trace amounts can be found. Below is a list of the top 8 gases, in order of the percentage of the atmosphere they each make up.

Gas	Percent of atmosphere
Nitrogen	78.084
Oxygen	20.946
Argon	0.934
Carbon dioxide	0.0397
Neon	0.001818
Helium	0.000524
Methane	0.000179
Krypton	0.000114

Observation

Earth can be seen from a number of locations in the Solar System, including the outer planets Jupiter and Saturn. From the Moon, Earth is clearly visible and appears to be much bigger than the moon ever appears from Earth. 

On 19 July 2013, new photographs surfaced from NASA of the Earth and moon viewed from Saturn's rings. The image was clearer due to the fact that the light reflecting from Saturn, which increased the clarity of the photograph. Currently, Earth is only thought to be visible from just beyond the orbit of Saturn, although it may be visible from Uranus and beyond with binoculars of a telescope.