Many carbonaceous chondrite meteorites, the very building blocks of planets, contain between several percent and up to 15% water by mass, locked within their clay minerals, according to Water Reservoirs in Small Planetary Bodies: Meteorites, Asteroids.... For decades, this fact fueled the prevailing theory that Earth's oceans were primarily delivered by water-rich asteroids. However, new evidence suggests Earth itself can generate significant amounts of water from its interior, challenging this long-held perspective. The origin of Earth's oceans is thus a more complex interplay of external delivery and internal planetary processes than previously understood, suggesting water might be more common on rocky planets than once imagined.
The Asteroid Hypothesis: A Cosmic Delivery Service
Isotopic evidence strongly supports the contribution of water-rich space rocks to Earth's early oceans. CI and CM group meteorites, linked to C-type asteroids, are often considered more probable sources of hydrogen and nitrogen for terrestrial planets than comets, based on their isotopic signatures, according to Water Reservoirs in Small Planetary Bodies: Meteorites, Asteroids.... Yet, Comet Wirtanen exhibits a water ratio identical to Earth's oceans, according to Comet Provides New Clues to Origins of Earth's Oceans. This persistent isotopic discrepancy fuels an ongoing debate: while specific meteorite groups are often favored, cometary similarities cannot be dismissed. The implication is that the precise external source remains elusive, possibly involving multiple contributors.
Earth's Inner Well: A New Source of Water
New research reveals rocky planets like Earth can generate water internally from magma oceans, hydrogen, and geological processes, according to Where Did Earth Get Its Oceans? Maybe It Made Them Itself.. The understanding of planetary hydration fundamentally shifts from solely external delivery to significant internal production. The implication is profound: companies focused on asteroid mining for water resources may be overlooking a more fundamental truth—rocky planets might be self-hydrating, potentially altering the economic calculus for future space exploration and resource acquisition.
