National Geographic : 1969 Dec
Yet they showed no ill effects whatever. This and other experiments indicate that the rock sample containers were no Pandora's boxes after all, despite early qualms. * The age of the Sea of Tranquillity appears to be extremely great-almost as old as the moon itself-to the surprise of many geolo gists. These rocks, dated by the rate at which radioactive potassium has been converted into argon, seem to have crystallized in their present form about three billion years ago.* (The moon, like the rest of the solar system, is estimated to have been formed about 4.6 billion years ago.) * High temperatures-higher than 2,200° F. -attended the birth of these rocks. The mate rial filling the Sea of Tranquillity is igneous (fire-formed), and was once molten, but wheth er it erupted from volcanic fires below the sur 790 Full of holes as Swiss cheese: When this moon rock cooled from molten material, gases within formed bubbles, or vesicles. The texture tells pe trologists that the rock cooled quickly near the lunar surface, but leaves unanswered a tantalizing question: whether melting resulted from volcanism or from meteorite impact. The drab 3/4-inch-wide chunk of rock explodes with color when a section only as thick as a man's hair is illuminated with polarized light (below). Magnified about 110 times, the wafer reveals min erals familiar on earth but combined differently ilmenite (black), pyroxene (purple, yellow, and blue), and plagioclase feldspar (white). Identification of minerals by polarized light was described in the Janu ary 1966 GEOGRAPHIC. Glossy-topped lumps (right), photographed on the moon, appear glazed by great heat. They suggest to Professor Thomas Gold of Cornell that a giant flare-up of the sun within the past 100,000 years scorched the moon. The earth escaped scorching because of the protection of its atmos phere, equivalent to about NASA; 2/3 TIMESACTUALSIZE 10 feet of rock. Professor Gold thinks the solar out burst may have been caused by an asteroid or huge comet striking the sun. Moon explorers Armstrong and Aldrin noted many such glassy-topped protu berances in small craters whose steep sides would have focused the heat. Armstrong shot this and 16 other pictures with a close-up stereo camera (page 768) made by Eastman Kodak to specifications of a team of scientists headed by Professor Gold. face or was melted by cataclysmic impacts of meteorites is not settled. * The moon is virtually paved with bits of glass, much of it in irregular fragments. Glass makes up fully half of the moon-soil sample brought back to earth. About 5 percent of the glass consists of delicate globules and tear drops that show beautiful shades of brown, green, wine-red, and lemon (page 789). * Erosion processes that may be like sand blasting have rounded and smoothed the sur faces of rocks. Most of the specimens show tiny glass-rimmed pits or glassy splotches. Is this from a continual rain of meteorites? The explanation is still not clear, says Dr. Paul W. Gast of the Lamont-Doherty Geological Ob servatory, chairman of the group of scientists *See "A Clock for the Ages: Potassium-Argon," by Gar niss H. Curtis, NATIONAL GEOGRAPHIC, October 1961.