Earth is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. It is the largest and densest of the solar system's terrestrial planets. Scientists estimate that the Earth was formed around 4.57 billion (4.57×10⁹) years ago.^[1] About 70 percent of the surface is presently covered by oceans, and the remainder consists of continents and islands. The abundance of water is a unique feature that distinguishes our "blue planet" from others in the solar system.

Since its formation, the Earth has been transformed through various geological and biological processes. The Earth's upper layer (lithosphere) is divided into several tectonic plates that gradually migrate across the surface over geologic time spans. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries. The interior of the planet is also active, with a thick layer (mantle) of highly viscous material and an iron core that generates a magnetic field.

The Earth is the only place in the universe known to support life, and its position, structure, and composition make it ideally suited for this purpose. Orbiting the Sun at an appropriate distance, this planet receives the proper amounts of heat and light to sustain life, and its rotational and orbital movements allow for daily and seasonal cycles. Its natural satellite, the Moon, is sufficiently large to produce regular tides and to stabilize the planet's axial tilt. In addition, the atmosphere provides useful gases, transports water vapor, moderates temperature extremes, absorbs harmful ultraviolet radiation, and burns up most meteors before they can strike the Earth's surface. The Earth's magnetosphere shields the surface by deflecting charged particles brought by the solar wind. The presence of water and the chemical composition of the Earth's surface play significant roles in the development and sustenance of living organisms. At the same time, the Earth's surface conditions have been significantly altered by the presence of life forms, which have created an ecological balance.