Is there any physical evidence for the theory that comets have caused mass extinctions on Earth?
There IS physical evidence, now. Scientists at a recent news conference sponsored by NASA presented compelling evidence that a comet collided with Earth about 250 million years ago, causing a massive explosion that killed 90 percent of all marine species and 70 percent of land species. The researchers found molecules of "stardust," containing trapped gases that could only come from outer space, in ancient sediments laid down at several locations around the planet at the time of the cataclysm. These molecules, known as fullerenes or "Buckyballs," contained a distinctive mix of the gases helium and argon that is found only in space. ---
Is this comet believed to have wiped out the dinosaurs?
No, this is ANOTHER huge, falling space object--one that would have occurred before the dinosaurs roamed the planet. This comet would have hit between the Permian and Triassic periods of geologic time and is probably the worst of five similar catastrophes that are believed to have occurred during Earth's prehistory. The fifth catastrophe, perhaps caused by an asteroid, is the one that may have killed the dinosaurs. Worse yet, researchers speculate that a catastrophic collision with a space object is an event that occurs about every 100 million years. According to scientist Christopher Chyba, a civilization may have a finite period of time to develop technology to avoid the threat of a major impact. The good news, says Chyba, is that scientists believe they have identified all of the major objects that could threaten Earth and about 40 percent of the medium-sized ones, and we're not due for a hit anytime soon. ---
How big do scientists believe the comet was?
Four to eight miles across--big enough to spew the fullerenes globally. How would you like THAT falling on you? The impact of a space object that big may have triggered volcanic eruptions that spewed dust and grit into the atmosphere. That, in turn, may have triggered global warming and downpours of acid rain or perhaps a chilly everlasting twilight. ~SUDDEN FACTS
~Thunderhead
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