Question

Which two reasons were thought to have rid Earth of its early water?

Answer 1

There are two reasons that are thought to have rid Earth of its early water: Mars lost its water due to a dropping temperature and loss of necessary greenhouse effect, while Venus lost its water due to a runaway greenhouse effect. Earth managed to maintain a delicate balance to keep liquid water on its surface. The water on Earth may have come from interstellar grains and/or from asteroids and comets that impacted the planet.

Step-by-step explanation:

There are two reasons that are thought to have rid Earth of its early water. One reason is that early in its history, Mars had a thick atmosphere with abundant liquid water, but it could not retain those conditions. The CO₂ necessary for a substantial greenhouse effect was lost, the temperature dropped, and eventually the remaining water froze. On Venus, the opposite happened, with a runaway greenhouse effect leading to the permanent loss of water. Only Earth managed to maintain a delicate balance that permits liquid water to persist on its surface.

Another possible reason is that the water on Earth may have come from interstellar grains. Water is abundant in dense interstellar clouds, and since stars are formed from this material, water must be present when solar systems, including our own, come into existence. The water in our oceans and lakes may have come initially from water locked into the rocky material that accreted to form Earth. Alternatively, the water may have been brought to Earth when asteroids and comets later impacted it.

Answer 2

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Step-by-step explanation:

There are two prevailing theories: One is that the Earth held onto some water when it formed, as there would have been ice in the nebula of gas and dust (called the proto-solar nebula) that eventually formed the sun and the planets about 4.5 billion years ago.