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Seesawing gas kept Earth frozen for longer

发布时间:2019-02-28 06:13:04来源:未知点击:

A PUZZLING shift in glacial cycles that occurred 950,000 years ago could be partially explained by changing greenhouse gas levels. Earth has spent most of the last 2.5 million years in an ice age, interrupted periodically by interglacial thaws that have warmed the planet to temperatures similar to today’s. These warm spells used to come every 41,000 years, but about 950,000 years ago the period shifted to every 100,000 years. Changes in ocean circulation or in the structure of continental ice sheets have been blamed for the shift. But David Lea of the University of California,