Final answer:
The early atmosphere's high concentration of water vapor decreased as it condensed to form clouds and rain, with the majority being absorbed by the oceans. Over time, our planet's bodies of water became a vast repository for this vapor, playing a significant role in Earth's water cycle and carbon capture.
Step-by-step explanation:
When the Earth's early atmosphere had formed from volcanic gases, it contained a higher concentration of water vapor compared to what we have now. The water vapor in the atmosphere condensed to form clouds and eventually rain, which led to the formation of oceans. The majority of the water vapor from the early atmosphere is currently absorbed by oceans. Oceans act as a reservoir for water vapor and also play a critical role in the carbon cycle, where carbon dioxide (CO₂) can be dissolved in the water.
Moreover, a future scenario has been depicted where, due to the action of sunlight breaking down water vapor in the upper atmosphere, Earth might eventually lose a substantial amount of its water vapor to space. However, this refers to a process that is projected to happen around 1 billion years from now, and not an event that reduced the water vapor in the early atmosphere. As such, water trapped in the Earth's crust or converted to ice, while significant, does not account for the majority of the reduction from the early atmosphere's water vapor levels.