The current trend of global warming is pushing Earth back from its ice Age "icehouse" conditions-with large ice sheets and many glaciers-to a "greenhouse" with little ice overall, Barker noted.
Current estimates suggest that half of all the living matter on Earth lives underground, at depths of up to 5km.
现在估计地球上大约一半的生物生活在地下深度约5千米以下的地方。
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The energy captured by space-basedphotovoltaic arrays would be converted into microwaves for transmissionto Earth, where it would be transformed into direct-current electricity.