The Earth may once have been surrounded by rings, like Saturn, which would have cast a shadow on parts of the planet all day long. The rings could have been formed after a glancing blow from an asteroid, when a space rock carves debris from a planet, then bounces off into the atmosphere. The resulting debris would also have shot off into space, and some of it would have ended up orbiting the Earth, forming a ring.

Peter Fawcett of the University of New Mexico and Mark Boslough of Sandia Labs say the debris ring would have cooled the planet by blocking or reducing the amount of sunlight it received in the tropics and subtropics. The rest of the planet would cool down too, because less heat would be transported from tropical regions to higher latitudes.
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Human beings are demanding more of the Earth than it cancope with, according to new research?and we?ve had 50% moreimpact on it in just the last 40 years. One of theresearchers, Mathis Wackernagel of Oakland, California,claims that by 1961, we were using 70% of the capacity ofthe global biosphere. By 1999, that had risen to 120% of theEarth’s productive capacity. In other words, we were using upresources faster than they could be replaced. The researchteam believes that ?human activities have exceeded thebiosphere?s capacity since the 1980s.?
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