Did Earth’s Water Come From Space?

The origin of Earth's water is explored, presenting competing hypotheses about its source. It was initially believed that Earth was dry and water was delivered later by comets, but the deuterium to hydrogen ratio in comets didn't match Earth's water. Asteroids, specifically carbonaceous chondrites, became a more compelling source due to their similar isotopic ratios. Another hypothesis suggests water formed on Earth itself through reactions between a hydrogen-rich atmosphere and iron oxides in the early magma ocean, a theory supported by recent lab experiments using a diamond anvil cell to simulate early Earth conditions. Determining the true origin requires further data, including isotopic measurements from asteroids/comets and observations of water on exoplanets. Michael Wong, an astrobiologist and planetary scientist, provides expertise on the topic.