What was the condition for water to remain on early Earth's surface?

Correct answer: Sufficient cooling of the surface

The direct answer is A: the early Earth's surface had to cool sufficiently for water to remain. Early Earth was extremely hot because of accretion, impacts, volcanic activity and internal heat. At very high temperatures, water could remain as vapour rather than stable liquid water. As the surface cooled, water vapour condensed into liquid water, and rainfall helped collect it in low areas to form oceans. Option A is correct because cooling is the necessary condition named in the question. Option B is wrong because all gases did not need to disappear; the atmosphere remained important. Option C is wrong because the core coming outside would destroy surface stability and is not a condition for oceans. Option D is wrong because solar wind does not become oceans. The chain is: hot surface, cooling, condensation, rainfall, collection of liquid water. Exam cue: liquid water requires suitable, not extremely high, temperature.