Earth is the only planet where water can exist on the surface in liquid form. Liquid water is essential for life as we know it. The oceans capacity for heat is very important in keeping the planet's temperature stable. To its detriment, liquid water is also responsible for most of the erosion and weathering of the continents.

Oceans at least 4 km deep cover nearly 70 percent of Earth's surface. Fresh water exists in the liquid phase only within a narrow temperature span. (0 degrees to 100 degrees Celsius). This temperature span is especially narrow when contrasted with the full range of temperatures found within the solar system. The presence and distribution of water vapor in the atmosphere is responsible for much of Earth's weather.

The Earth's atmosphere is 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water. The small amount carbon dioxide in the atmosphere is extremely important to the maintenance of the Earth's surface temperature via the greenhouse effect. The greenhouse effect raises the average surface temperature about 35 degrees C above what it would otherwise be. Without it the oceans would freeze and life as we know it would be impossible. Interestingly, water vapor is also a greenhouse gas.

Oxygen is a very reactive gas which under normal circumstances would quickly combine with other elements. The oxygen in Earth's atmosphere is produced and maintained by biological processes. In otherwords, without life, there would be no free oxygen.

The atmosphere affects Earth's long-term climate and short-term local weather. It shields us from nearly all harmful radiation coming from the Sun and protects us from meteors as well. (Most meteors burn up before they can strike the planet's surface).

Satellites have revealed that the upper atmosphere actually swells by day and contracts by night due to solar activity.

Our planet's rapid spin and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape. (The solar wind is a stream of charged particles continuously ejected from the Sun). The magnetic field does not fade off into space, but has definite boundaries. When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and are known as the aurorae, or the Northern and Southern Lights.

This magnetic field's interaction with the solar wind also produce the Van Allen radiation belts. They are a pair of doughnut shaped rings of ionized gas (or plasma) trapped in orbit around the Earth.

The Earth's core is composed mostly of iron or nickel/iron. It is probable that lighter elements are also present. Temperatures at the center of the core may hotter than the surface of the Sun. As hot as 7500 K or over 13,000 degrees.

The lower mantle is mostly silicon, magnesium and oxygen. Other elements such as iron, calcium and aluminum are also present. The upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium and aluminum. The crust is primarily quartz, (silicon dioxide), feldspar and other silicates. In its entirety, the Earth's mass is composed of the following approximates:

• 34.6%  Iron
• 29.5%  Oxygen
• 15.2%  Silicon
• 12.7%  Magnesium
• 2.4%  Nickel
• 1.9%  Sulfur
• 0.05% Titanium

Earth's crust is divided into eight separate solid plates which float around independently on top of the hot mantle below.

The Earth is the densest major body in the solar system.

Moon of Earth