Mean Distance from sun (Earth = 1) - 1,

Earth, is a differentiated planet with a dense iron-rich core that is still partially molten, a thick mantle of iron- and magnesium-rich silicates, and a crust of silica-rich and magnesium-poor rocks. Much of the knowledge of the interior structure of the Earth comes from interpretation of seismic data. Earth's lithosphere is ten to several hundred kilometers thick and is thinner and more mobile than that of the Moon, Mercury, or Mars.

As indicated by the relative lack of cratering, most of the surface of the Earth is relatively young. Oceanic crust is at most approximately 200 million years old. By contrast, the age of continental crust can be much older, including the oldest rocks on Earth (just over 4 billion years old). Continental crust is less dense than oceanic crust and once formed tends to remain on the surface of the planet. The evolution of our current surface is the result of Plate Tectonics (see below).

The atmosphere is poor in carbon dioxide, rich in the residual nitrogen, and also rich in oxygen. Carbonate rocks contain a great deal of the CO₂ observed in the atmospheres of other planets. The oxygen is the direct result of life, the origin of which can be traced back to about 3.8 billion years ago.

The magnetic field produced by electric currents in the outer core; the polarity of the field has changed many times over geological history. On average the reversal rate for Earth is on the order of once every few hundred thousand years but the actual time between reversals can vary greatly. The last reversal was about 780,000 years ago. The extensive magnetic field and the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun.

Plate Tectonics (the really short version)

Plate tectonics involves the formation, lateral movement, interaction, and destruction of the lithospheric plates that form the surface of the Earth. It is the method by which the Earth relieves itself of internal heat. Convection currents in the mantle are responsible for the motion of the plates. Relative velocities of plates are on the order of 5-15cm per year. Most earthquakes, volcanic eruptions and mountain ranges can be directly related to the interactions at the edges of these large plates.

Divergent: plates move apart, surface material is created (Mid Atlantic ridge)

Convergent: plates come together, surface material is consumed (Japan or Chile-Peru Trench)

Transform: Plates slide past each other, no surface material is destroyed or created (San Andreas Fault)

Plate motion and the repeated cycles of ocean basin formation and closing shaped the present appearance of the planet's surface and ensure that the surface of the planet changes continuously (though, fortunately for us in geological time).

The Earth/Moon interaction that causes the Moon to recede also slows the Earth's rotation by about 2 milliseconds per century. Good evidence indicates that about 900 million years ago there were 481 18-hour days in a year.