Ocean and Atmosphere on Early Earth

Where did Earth’s ocean water come from? Scientists agree that a large amount of water must have arrived during planet, accretion, which is the process of collision and sticking together of the material in orbit around the Sun by which Earth and the other planets in the solar system formed 4.6 billion years ago. Perhaps significant volumes were added during the period of heavy bombardment, during which Earth was being hit by a large number of comets (whose nuclei are composed mostly of ice) and other objects left over from the formation of the planets. The volume of water eventually found on Earth may be related to the formation of Earth’s core (innermost layer). When the iron- and nickel-rich core formed, most of the water in the forming planet was consumed in oxidation processes whereby the oxygen component of water was used to make iron and nickel oxides. It is the residual water that make up the oceans. Perhaps that residual quantity was significantly enhanced by water carried by comets after Earth’s initial formation, perhaps not .1n either case, the oceans reached approximately their present volume by 3.8 billion years ago. But this does not mean they were at their present area. Geologist Don Lowe has estimated that before 3 billion years ago, less than 5 percent of Earth’s surface was land. Earth’s atmosphere was also very different from that of today. There was no oxygen, and there was a great d.1 more carbon dioxide (Co2)—perhaps 100 to 1,000 times as much as today.

Earth’s surface temperature was higher than it is now because more heat was emanating from the interior and because of the warming generated by the extensive CO2 and other greenhouse gases in the atmosphere. Greenhouse gases trap heat near the surface through the so-called greenhouse effect. Earth’s internal generation of heat was an important factor; the Sun at this time was much fainter, a delivering perhaps a third less energy, than at the present time.

What would have happened if Earth had stayed a water world? Probably global temperatures would have remained high or even increased. For animal fife to form, the temperature had to drop from the levels acknowledged to have been characteristic of Archaean time (about 4 to 2.5 billion years ago).A drop in global temperature while the Sun was getting hotter required a drastic reduction of atmospheric CO2–a reduction of the greenhouse effect. Thus there had to be some means of removing CO2.The most effective way to do this is through the formation of limestone, which uses CO2 as one of its building blocks and thus removes it from the atmosphere. But significant volumes of limestone form today only in shallow water; the most effective limestone formation occurs in depth of less than 20 feet (6 meters),In deeper water, high concentrations of dissolved CO2 slow or inhibit the chemical reactions that lead to limestone formation. There is evidence of deep-water, inorganic limestone formation in very old rocks on Earth, as demonstrated by geologist Jo. Grominger and his team. These studies thow. that early Earth’s ocean may have been saturated in the compounds that can produce limestone and thus could have formed solid limestone in deeper water at that time, removing carbon dioxide from the atmosphere as a consequence. However, Grominger points out that occurrences of carbonate rocks such as limestone during the early Archaean–roughly the first billion years of Earth’s existence—are rare. And this is only partly due to the rarity of rocks of this age. It looks as though the central mode of removing carbon dioxide from the atmosphere-the formation of carbonate rocks—seldom occurred.

To form limestone in significant volumes, then, shallow water is needed, but on a planet without continents, shallow water is in short supply.On Earth from perhaps 2.7 to 2.5 billion years ago there occurred a rapid buildup of continental areas, resulting in an increase in the land surface from perhaps 5 percent to about 30percent.Larger continents meant larger shallow-water regions, for the emergence of continents created the shallow areas near the continents as well as large inland seas and lakes.?

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Where did Earth’s ocean water come from??Scientists agree that a large amount of water must have arrived during planet, accretion, which is the process of collision and sticking together of the material in orbit around the Sun by which Earth and the other planets in the solar system formed 4.6 billion years ago. Perhaps significant volumes were added during the period of heavy bombardment, during which Earth was being hit by a large number of comets (whose nuclei are composed mostly of ice) and other objects left over from the formation of the planets. The volume of water eventually found on Earth may be related to the formation of Earth’s core (innermost layer). When the iron- and nickel-rich core formed, most of the water in the forming planet was consumed in oxidation processes whereby the oxygen component of water was used to make iron and nickel oxides. It is the residual water that make up the oceans. Perhaps that residual quantity was significantly enhanced by water carried by comets after Earth’s initial formation, perhaps not .1n either case, the oceans reached approximately their present volume by 3.8 billion years ago. But this does not mean they were at their present area. Geologist Don Lowe has estimated that before 3 billion years ago, less than 5 percent of Earth’s surface was land. Earth’s atmosphere was also very different from that of today. There was no oxygen, and there was a great d.1 more carbon dioxide (Co2)—perhaps 100 to 1,000 times as much as today.