The origin and evolution of Earth involved physical processes that operate on all matter and energy in the universe. The formation of stars is a common phenomenon in galaxies, and the formation of planetary systems is a common result of star formation. Planets are extremely common throughout the universe, and the technology to detect and characterize them continues to improve. Almost 900 planets had been discovered as of the end of 2012, with even more candidates awaiting confirmation. Both the sizes and masses are becoming known for an increasing number of planets, allowing a preliminary division into rocky, icy, and gaseous classes.

In our solar system, three rocky planets had the potential early on for supporting life. Venus, Earth, and Mars were all endowed with carbon dioxide atmospheres, and at least Earth and Mars received large influxes of organic materials and water. The presence of a watery ocean was a key early step toward regulating and retaining the atmosphere. The absence or early demise of an ocean on Venus is causal to its present state: with no sink for carbon dioxide in the form of carbonates, all of the carbon dioxide remained as a massive atmosphere supporting a super-greenhouse warming: perpetually too hot to ever permit liquid water to exist.