Since plants had not yet evolved 700 million years ago, the dirty ice could have been the only dark spots on Earth's surface to absorb the sun's rays.

7亿年前地球上还没有植物，浑浊的冰（泥土和冰的混合物）可能是地球表面唯一能够吸收阳光的黑色物质。

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We have a pretty good idea that they're made of dirty ice, but beyond that, we don't really know the details of what they're made of.

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When the ice sheets were thick and advancing, more pebbles, stones, and dirty sediment would have been carried into the core by the moving ice.

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