### Origin of Earth's Water
How Earth acquired its vast oceans remains a central question in planetary science. Two models propose different origins:
Model 1 (Extraterrestrial Delivery)
Earth accreted as a dry planet because its orbit was inside the "snow line," where solar heat prevented ice from condensing. Earth's water was delivered later, during the Late Heavy Bombardment ( billion years ago), via collisions with water-rich comets and carbonaceous chondrite meteorites from the outer asteroid belt.
Model 2 (Endogenous Degassing)
Earth accreted with water already present, bound within the crystalline structure of mantle minerals (such as ringwoodite) in the early mantle. Over time, high temperatures and pressures forced water out of these minerals, and it was transported to the surface via volcanic outgassing during Earth's early history.
Based on the models described, match each new scientific finding on the left with its primary implication for these models on the right.
- Finding 1: The deuterium-to-hydrogen () ratio of Earth's ocean water is identical to that of carbonaceous chondrite meteorites, but is significantly lower than that of comets.Supports the chondrite component of Model 1 while contradicting the cometary component of Model 1.
- Finding 2: Seismic data and laboratory simulations reveal that transition zone minerals like ringwoodite can hold up to water by weight, enough to store multiple oceans in the mantle.Supports Model 2 by verifying the existence of a viable internal mineral reservoir capable of storing Earth's water.
- Finding 3: Analysis of ancient volcanic glass beads shows that the rate of primordial volcanic outgassing during the Hadean eon was insufficient to produce the volume of modern oceans.Contradicts Model 2 by demonstrating that volcanic outgassing alone cannot account for the total volume of Earth's oceans.