50.From a draft textbook manuscript submitted to apublisher. "As Earth was being formed out of the collision of space rocks,the heat from those collisions and from the increasing gravitational energy ofthe planet made the entire planet molten, even the surface. Any water presentwould have evaporated and gone off into space. As the planet approached itscurrent size, however, its gravitation became strong enough to hold gases andwater vapor around it as an atmosphere. Because comets are largely ice made upof frozen water and gases, a comet striking Earth then would have vaporized.The resulting water vapor would have been retained in the atmosphere,eventually falling as rain on the cooled and solidified surface of Earth.Therefore, the water in Earth's oceans must have originated from comets."
当地球在太空岩石的撞击作用下形成的时候,撞击产生的热量和行星越来越大的重力能量使整个行星融化,甚至包括表面。当时存在的任何水分都会蒸发并消失在太空。然而,当行星接近现在的大小的时候,它的重力强到了足以保持其周围的气体和水蒸气来形成大气层。由于彗星主要是由冻结的水和气体组成的冰,撞击地球的彗星将会蒸发。产生的水蒸气将被留在大气层,最终以降雨的形式落在地球已冷却而且坚硬的表面。因此,地球海洋的水分一定是来自彗星。
"As Earth was being formed out ofthe collision of space rocks, the heat from those collisions and from theincreasing gravitational energy of the planet made the entire planet molten,even the surface. Any water present would have evaporated and gone off intospace. As the planet approached its current size, however, its gravitationbecame strong enough to hold gases and water vapor around it as an atmosphere. Because comets arelargely ice made up of frozen water and gases, a comet striking Earth thenwould have vaporized. The resulting water vapor would have been retained in theatmosphere, eventually falling as rain on the cooled and solidified
surface of Earth. Therefore, the water in Earth's oceans must have originatedfrom comets."