The remaining 29% is land consisting of continents and islands that together have many lakes, rivers and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack.
In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk along with the Sun.
The origin of the world's oceans was condensation augmented by water and ice delivered by asteroids, protoplanets, and comets.
Continents formed by plate tectonics, a process ultimately driven by the continuous loss of heat from Earth's interior.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant.
Another convention capitalizes "Earth" when appearing as a name (e.g.