INCREASES in the amount of dust and meteors falling into the Earth鈥檚
atmosphere may have caused the ice ages, scientists say in last week鈥檚
Science (vol 277, p 215).
Ice ages have usually been put down to periodic changes in the Earth鈥檚 orbit
that alter the amount of sunlight reaching the northern hemisphere. This should
bring about cold spells roughly once every 40 000 years.
But Rich Muller of the Lawrence Berkeley Laboratory in California and a
colleague say that the ice ages occurred every 100 000 years. They reached this
conclusion after looking at sediments from eight locations worldwide.
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Muller says that the period of 100 000 years matches the cycle in which the
Earth moves above and below its normal plane of orbit. This wobble alters the
influx of meteors and dust, and hence the amount of sunlight penetrating the
atmosphere. However, Muller concedes: 鈥淲e don鈥檛 have a detailed theory of how it
affects climate.鈥�