Why is the current D/H ratio of Earth's ocean actually higher than what Earth possessed when it first formed?

Answer

Lighter hydrogen atoms escape into space more readily than deuterium during atmospheric loss

Atmospheric escape processes are more efficient at removing the lighter isotope (H) than the heavier isotope (D), causing the relative proportion of deuterium remaining in the oceans to increase over time.

Why is the current D/H ratio of Earth's ocean actually higher than what Earth possessed when it first formed?
OriginEarththeorywatercomet