The Earth and its Oceans 

 T. F. Gaskell 



If the Earth were formed from four to five thousand million 

 years ago, as we now believe, and if the oceans were formed soon 

 afterwards, then our planet's mantle of water is very old. Even 

 though we have no direct evidence of what happened in those misty 

 beginnings, we can deduce a sequence of events that might account 

 for the formation of our planet and its restless seas. 



On the one hand, the Earth and its companion planets making 

 up the solar system could have been formed cold — as a result of 

 large nuclei of matter sweeping up gas, dust, and solid particles 

 spread out around the newborn Sun. Over millions of years this 

 sweeping-up process would have continued, each planetary nucleus 

 capturing and drawing into itself larger and larger aggregates of 

 matter. 



On the other hand, according to a quite different theory, the 

 Earth was formed hot, having condensed from a whirling mass of 

 hot gaseous material thrown off from the Sun. Whether the Earth 

 was formed hot or cold, there is little doubt that soon after its 

 formation it became a molten globe. If not, then we have no satis- 

 factory way to explain the distribution of heavy and light matter 

 within our planet. We now know that the core is made up of the 

 densest material, iron-nickel, and has a diameter of about 4000 

 miles. Surrounding the core is the mantle, 2000 miles deep and 

 made up of lighter silicate rocks rich in iron and magnesium. The 

 outer shell of the Earth, a five- to twenty-mile-thin crust, is made up 

 of still lighter rocks — the kinds we see at the surface. 



As a molten globe, the Earth would have lost heat rapidly. In 

 about 10,000 years it would give off enough heat to allow a sub- 

 stantial part of the crust to solidify. It was sometime during this 

 infant stage in the Earth's life that the oceans began to form. At 

 first, the water that later flowed into land basins was locked up in 

 the molten rock since at high temperatures and pressures water and 

 rock can mix in any proportion. But as the primordial rock cooled 

 and solidified, the water was squee2ed out, evaporated, and added 

 to the Earth's primeval atmosphere. It was a fortunate chance that 

 the Earth was large enough to retain its atmosphere, for unless a 

 planet is of a certain minimum size it cannot hold an appreciable 

 atmosphere by gravitational attraction, so the atmosphere will leak 

 off into space. There is no atmosphere to speak of on the Moon, 

 and relatively little on Mars. 



While the crust was cooling and giving off water vapor to the 

 atmosphere, massive clouds formed and released rain in torrents. 

 For how many tens or hundreds of years the first rains poured 

 down onto the cooling crust - first steaming back into the atmos- 

 phere because the surface rocks were still above the boiling point 

 of water — we cannot say. But gradually the surface rocks grew 

 cool enough so that the rains no longer boiled away. The waters 

 collected in pools, cascaded into depressions and flowed as rivers, 

 sculpturing the land and ever seeking the lowest levels. Gradually 

 the first basins began to fill, but they were not the sea and ocean 

 basins we know today. 



"And the spirit of God moved upon ttie face 

 of tlie waters." This medieval impression of 

 the Creation Story is depicted in a mosaic 

 of 1182 in the dome of Monreaie Cathedral, 

 Sicily. (Only a section is shovi/n here.) 



