Overview (The Solar System)
Of all the planets in the solar system, Earth stands out as basically a watery world, distinguished from the other planets by large quantities of liquid water. In all, Earth has about 1.36 billion cubic kilometers of water, and 97.2 percent is stored in the oceans. The remaining 2.8 percent of Earth’s water not in the oceans is apportioned among ice (77 percent of the total remaining water) and continental and atmospheric waters. The ice itself, now principally in the Arctic-Greenland area (1.72 million square kilometers, up to 3,200 meters thick) and the Antarctic area (12 million square kilometers, up to 4,000 meters thick), has effects ranging from climate control to providing habitats for living organisms to being a reservoir for water that, when added to or removed from the oceans in the past, has caused sea level to rise or fall more than 100 meters.
Ocean water is salty because it contains dissolved minerals; with a salinity of 35,000 parts per million, there is enough dissolved salt to cover the entire surface of the Earth to a depth of about 50 meters. This salty solution is composed primarily of sodium and chlorine ions (together constituting about 86 percent of the ions by weight), along with ions of magnesium, calcium, potassium, and sulfate and carbonate groups. Seawater is slightly basic, with a pH of 8 for the hydrogen-ion concentration.
The problem of the oceans’ origin is twofold: (1) the primordial...
(The entire section is 1535 words.)
Methods of Study (The Solar System)
Numerous avenues of approach have been used to investigate the ocean and its ions, including geological, chemical, and physical means. Geology has supplied basic data on the types and makeup of rocks from the earliest solidified materials to present depositional formations. Use of the petrographic microscope, involving thin sections of rocks seen under polarized light, allows the identification of minerals, providing quantity measurements of water attached to the minerals themselves. Paleontological studies of fossil organisms and paleosoils indicate the range of ions in the sea at diverse geologic periods, both by the ions themselves left in the deposited soils and rocks and through studies of the tolerance ranges for similar, twentieth century organisms. Such studies—along with sedimentological investigations of rates and types of river depositions, dissolved ion concentrations, and runoff rates for falling rain—provide determinants for comparing ion concentrations with those in the past for continentally derived materials.
Chemical analysis reveals the various ions present in seawater and rocks via two principal methods. The mass Spectrometer identifies types and quantities of ions present by use of a Magnetic field to accelerate the charged ions along curved paths, the curvature of the paths based on the weight and charge of the ions. Collection at the end of the paths provides pure samples of the different ions...
(The entire section is 514 words.)
Context (The Solar System)
Water is a ubiquitous and by far the most important molecule on Earth. All living organisms require it as a basic component of cellular structure and for numerous functions inside the body. The origin of Earth’s water is highly significant, because the very presence of water may have set the scheme for all subsequent evolution, both geological and biological, on the planet. During the formation of the solar system, the accretion of various materials trapped water by hydration. Tied to the minerals, the water molecules were released through outgassing by volcanoes and other vents acting as pressure escape valves for the molten interior of the Earth. The water and other Volatile gases that were released formed the atmosphere and subsequent oceans. A vital interchange was established between the ground and the atmosphere, one replenishing elements and compounds as they were lost through Geochemical sinks in the normal course of history. Water, at first in the atmosphere, then as liquid seas, apparently helped to mediate the greenhouse effect, a mechanism which, if allowed to act unhindered, would have trapped Infrared radiation from the Sun and overheated the early Earth. Such actions would have given the Earth the characteristics of the planet Venus: enormously hot and totally inhospitable for life’s occurrence.
The outgassed water, settling as rain, also played the dominant role in shaping the landforms of Earth. As a mechanism...
(The entire section is 386 words.)
Further Reading (The Solar System)
Brancazio, Peter J., ed. The Origin and Evolution of Atmospheres and Oceans. New York: John Wiley & Sons, 1964. This work is a collection of papers dealing with the chemical problems relevant to the early formation of the fluid parts of the Earth. Tracing all the basic arguments, the criteria for water formation is clearly explained and its relationship to minerals and rocks elucidated. Some heavy reading, charts, extra references.
Chamberlain, Joseph W. Theory of Planetary Atmospheres: An Introduction to Their Physics and Chemistry. New York: Academic Press, 1978. A detailed analysis of the characteristics of diverse atmospheres in the solar system, including water contents. By comparisons of chemical compositions and meteorological observations, criteria are established for examining the possible origins for atmospheric gases and oceans. Some mathematics, heavy reading, numerous charts, comprehensive references.
Consolmagno, Guy. Worlds Apart: A Textbook in Planetary Sciences. Englewood Cliffs, N.J.: Prentice-Hall, 1994. An introduction to planetary science for beginners and undergraduates. Covers all planets in the solar system.
Frakes, L. A. Climates Throughout Geologic Time. New York: Elsevier, 1980. A well-written explanation of how the interaction of the Earth’s atmosphere and oceans has caused the climate of the Earth to change over the history of the planet....
(The entire section is 694 words.)