Review Essay Example | Topics and Well Written Essays - 500 words - 11

Review - Essay Example These theories are concerned with the bombardment of the Earth by â€Å"icy clumps of material† (30), or planetismals. This collision results in the formation of steam in the atmosphere. After some steam being ejected into the sky, and some being split by ultraviolet radiation, sufficient steam remains in the atmosphere to condense and form the oceans when the Earth cools. The origin of these planetismals is subject to different viewpoints. They are variously argued to be asteroids, comets and meteorites. Plate tectonics is responsible for the creation and present configuration of the ocean basins, which serve as containers to hold water. This process agitates the Earth’s mantle, separating it into the lighter granitic rock which floats on top to form the continents, and the heavier basalt which sinks to form the ocean basins. The Earth’s orbit is another important factor for the presence of water. To one side of the Earth, Venus is so close to the sun, that water evaporates skyward, and is split by the sun’s ultraviolet rays into hydrogen which is lost into the sky. On the other side, Mars is too far from the sun and remains frozen due to runaway glaciation. Unlike its neighbors, the Earth’s orbit lies in the ‘habitable zone’, with regard to its distance from the sun, thus permitting the presence of liquid water. The Earth’s stratified atmosphere, due to the significant presence of carbon-dioxide and methane, which absorb infrared radiation, results in the greenhouse effect, keeping the planet warm even during the age of the early, faint sun. This prevents the loss of water and hydrogen into the sky. Volcanism is the last factor which contributes to the presence of water on Earth, due to the carbonate-silicate cycle. Volcanism gives the Earth a â€Å"built-in (geochemical) thermostat† (33), which regulates the Earth’s climate and maintains the surface temperature in a range