Earth, also known as the Earth or Terra, is the third planet outward from the Sun. It is the largest of the solar system's terrestrial planets, and the only planetary body that modern science confirms as harboring life. The planet formed around 4.57 billion (4.57Ç_109) years ago and shortly thereafter acquired its single natural satellite, the Moon. Its dominant sentient species is the human (Homo sapiens sapiens).

Its symbol consists of a circled cross, representing a meridian and the equator; a variant puts the cross atop the circle. The Earth is approximately a slightly oblate spheroid, with an average diameter of approximately 12,742 km. The maximum deviations from this are the highest point on Earth (the summit of Mount Everest, which is only 8,850 m) and the lowest (the bottom of the Mariana Trench, at 10,911 m below sea level).

Thus the Earth is an oblate spheroid within a tolerance of one part in about 584, or 0.17 %. The mass of the Earth is approximately 6,000 yottagrams (6 x 1024 kg).

The interior of Earth, like that of the other terrestrial planets, is chemically divided into an outer siliceous solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The liquid outer core gives rise to a weak magnetic field due to the convection of its electrically conductive material.