For the time before records began, we have only "proxy records" reconstructed largely from tree rings and icecores, supplemented by a few incomplete written accounts.
在开始有记录之前,我们只有主要根据年轮和冰芯重建的“代理记录”,还有一些不完整的书面记录作为补充。
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Recent expeditions have taken ice samples from green icebergs and icecores—vertical, cylindrical ice samples reaching down to great depths—from the glacial ice shelves along the Antarctic continent.
Such icecores trap gases, bits of dust, and other chemicals that were present in the snow that fell over Greenland for thousands of years and then became compressed into ice.