Some scientists hypothesize that icy debris arrived on other terrestrial planets in a similar manner to how it arrived on Earth. On Earth, the ice eventually turned to water and water vapor, forming extensive oceans and a life-sustaining atmosphere. But the same is not exactly true for the other terrestrial planets. What are two reasons why? Temperatures on Earth are ideal for water to exist in solid, liquid, and gaseous forms.
Magnetic forces generated in Earth’s mantle are directly responsible for Earth’s oceans.
Earth’s gravity holds the water vapor in Earth’s atmosphere close to its surface.
Earth’s solid outer core is sufficiently rigid to keep water above its surface.