Word: asteroidal
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Dates: during 1980-1989
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...surprise, it turned out to be 30 times as rich in iridium as normal rocks. The Berkeley team knew of only a few places where such high concentrations of the rare element might occur: in the earth's core, perhaps 2,000 miles belowground; in extraterrestrial objects like asteroids (or their fragments, meteors) and comets; or in the cosmic dust drifting to earth from a nearby supernova (exploding star). The core material seemed too deep to come to the surface, and further analysis ruled out a supernova as the source, so father and son concluded that the iridium had been...
...Alvarezes did not stop there. Basing their calculations on the atmospheric consequences of the explosion of Krakatoa, they roughly estimated how much dust the impact of the asteroid would have thrown into the atmosphere, how long sunlight would have been blocked from the earth's surface, and what kinds of life would have been the most gravely affected by the climatic changes. They decided that plants, totally dependent on the sun for photosynthesis, and a variety of marine organisms would have died first, followed by the land animals highest on the food chain, the dinosaurs. Eventually the iridium-enriched debris...
...about stars and periodicity, when Muller noted that more than half the stars in the galaxy are thought to be binaries (pairs of stars that orbit a common center of gravity). Suppose the sun has a companion, he mused, and that companion was somehow disrupting the solar system's asteroid belt. Trouble was, he conceded, he could not come up with a convincing orbit for the companion. Suddenly the Dutch-born Hut interrupted him with an alternative suggestion: Why not make the companion star travel through the thickest part of the comet-filled Oort cloud, rather than the asteroid belt...
Although both comets and asteroids can wreak considerable havoc if they collide with the earth, they are of very different natures and origins. Asteroids are rocky chunks that range in size from pebbles to a mammoth named Ceres that astronomers estimate to be as much as 600 miles across. Most of them orbit the sun in a belt between Mars and Jupiter and are thought to be either remnants of a planet that disintegrated early in the life of the solar system or celestial building blocks that never quite coalesced into a planet. Occasionally an asteroid is slowed...
Even now, more than three-quarters of a century after the spectacular event at Tunguska, scientists are certain only that a celestial intruder was responsible. Some argue that it was an asteroid as large as 500 ft. across and weighing 7 million tons, which rapidly heated as it entered the earth's atmosphere and exploded about five miles above ground. Others believe it was a small comet. Whatever the cause, the destructive power of the object from space rivaled that of a very large nuclear warhead; scientists gauge the explosion at twelve megatons...