Which theories are proposed explanations for the origin of Earth's water?

Which theories are proposed explanations for the origin of Earth's water?

• A. Outgassing from Earth's interior
• B. Bombardment by comets and water-rich asteroids
• C. Both A and B
• D. Water formed during the planet's formation and remained in the mantle

Answer: (C)

Earth’s water likely comes from two main processes that both fit the evidence. First, outgassing: water is trapped in minerals and melts in the mantle, and volcanic activity releases that water vapor, which then condenses to form oceans. This explains how water became present on Earth as it differentiated and cooled. Second, delivery by water-rich bodies: during the early solar system, comets and asteroids containing ice collided with Earth and added substantial amounts of water. Isotopic measurements of Earth's ocean water (the hydrogen isotopic ratios) resemble those found in some carbonaceous chondrites, supporting this external delivery. Together, these ideas account for the amount of water and its isotopic characteristics. The notion that all water formed with Earth and stayed confined in the mantle doesn’t align as well with the evidence, which points to both internal release and external delivery contributing to the oceans.

Earth’s water likely comes from two main processes that both fit the evidence. First, outgassing: water is trapped in minerals and melts in the mantle, and volcanic activity releases that water vapor, which then condenses to form oceans. This explains how water became present on Earth as it differentiated and cooled.

Second, delivery by water-rich bodies: during the early solar system, comets and asteroids containing ice collided with Earth and added substantial amounts of water. Isotopic measurements of Earth's ocean water (the hydrogen isotopic ratios) resemble those found in some carbonaceous chondrites, supporting this external delivery.

Together, these ideas account for the amount of water and its isotopic characteristics. The notion that all water formed with Earth and stayed confined in the mantle doesn’t align as well with the evidence, which points to both internal release and external delivery contributing to the oceans.