In addition to outgassing by volcanoes, another important contributor to the formation the Earth's oceans and atmosphere was

Question

Quizplus · Accepted Answer

Impacts by icy planetesimals would have brought water to Earth in the form of ice, which would have melted upon impact and contributed to the formation of the oceans and atmosphere. Material directly accreted from the Sun or solar nebula would not have contained water, and melting and vaporization of polar glaciers would not have been a significant contributor to the formation of the oceans and atmosphere.

In Addition to Outgassing by Volcanoes, Another Important Contributor to the Formation