Much of the water on Earth,Venus,and Mars has come from outgassing of water vapor from volcanoes.Much of the remainder is believed to have come from
A) chemical reactions,which have produced water from more complex molecules.
B) the combination of elemental hydrogen and oxygen in the atmosphere,the reaction powered by high-energy ultraviolet rays.
C) baking of rocks containing water.
D) the impacts of comets.

Question

Quizplus · Accepted Answer

The best answer is D because it is widely believed that comets brought significant amounts of water to Earth, Venus, and Mars through impacts. This theory is supported by the fact that comets are mostly made up of water ice and other volatile compounds. While the other options may also contribute to the presence of water on these planets to some degree, the impact of comets is thought to have been a major factor.

Much of the Water on Earth,Venus,and Mars Has Come from Outgassing