Science: Pay Dirt from the Moon

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Pay Dirt from the Moon The crew of Apollo 11, the first men on the moon, brought back only 481 Ibs. of lunar rocks and dust. But even that small sampling from the Sea of Tranquillity has been enough to keep 142 scientists in the U.S., Canada, Japan, Australia and Western Europe fully occupied in their laboratories since late last summer. In Houston last week, at a symposium sponsored by NASA, the lunar investigators finally took time out from their work to report on what they had learned so far. Their findings add a vast store of fresh knowledge about the earth's nearest celestial neighbor, but leave unanswered most of the puzzling questions about the moon's origin and evolution.

Hot v. Cold. One of the more surprising revelations at the symposium was the age difference between the dust and the rocks found at Tranquillity Base. Using dating methods based on the decay of radioactive elements, scientists determined that, although the dust particles were 4.6 billion years old —the apparent age of the moon itself —most of the rocks were about 1 billion years younger. How could there be such a huge age gap between material picked up only a few feet apart? "This is a major puzzle," says Rice University Geologist Dieter Heymann. One small rock fragment, though, was considerably older than the others: 4.44 billion years. Caltech Geologist G. J. Wasserburg, who calculated its age, believes that still older rocks dating back to the very creation of the moon will probably be found in the unexplored lunar highlands.

Examination of the lunar rocks also established that catastrophic events rocked the moon about a billion years after its creation. "There were definitely lava flows 3.65 billion years ago," says Wasserburg. Scientists are still uncertain whether the lava rose from a hot lunar interior or was created by heat from the impact of huge meteorites. If the melting was indeed caused by meteors, a similar process might have occurred on the nearby earth. This could explain why scientists have been unable to find any terrestrial rocks older than 3.6 billion years—although the earth, too, is believed to be 4.6 billion years old.

Making Tracks. There were also some smaller surprises. Examining the lunar material with scanning electron microscopes, scientists observed that even the tiniest granules were cratered by micrometeorite bombardment. They also saw miniaturized versions of the larger glassy spheres spotted and collected by the Apollo astronauts; they were apparently formed by splashes of hot debris from meteorite impacts. Several scientists showed electron micrographs of pyroxenes (a mineral also found on earth) that had crystallized in a remarkable candy-stripe pattern. The investigators also saw tiny tracks produced in the rocks by the bombardment of cosmic ray and solar particles. Made millions and even billions of years ago, these markings are permanent records of the sun's activity. From them, scientists may learn, for example, if the earth's ice ages were in fact caused by long periods of reduced solar output.

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