Origin of water on Earth

Uncommon card · No. 78086

The Earth is unique among known planets in having oceans of liquid water on its surface. It was long thought that Earth's water did not originate from the planet's region of the protoplanetary disk. Instead, it was hypothesized that water and other volatiles must have been delivered to Earth from the outer Solar System later in its history. Recent research, however, indicates that hydrogen inside the Earth played a role in the formation of the ocean. The two ideas are not mutually exclusive, as there is also evidence that water was delivered to Earth by impacts from icy planetesimals similar in composition to asteroids in the outer edges of the asteroid belt. Liquid water, necessary for all known life, continues to exist on Earth's surface because the planet is at a distance (the habitable zone) from the Sun that allows it to retain water without freezing.

Read on Wikipedia · Image Reto Stöckli (land surface, shallow water, clouds) Robert Simmon (enhancements: ocean color, compositing, 3D globes, animation) Data and technical support: MODIS Land Group; MODIS Science Data Suppor…, Public domain