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Which Came First: Low CO2 or an Ice Age?
二氧化碳含量变低和冰河世纪哪个先来？
What starts an Ice Age? Clues exist in the remains of coccolithophores, a type of marine algae with a shell.
冰河世纪开始的原因是什么？线索在颗石藻化石中，颗石藻是一种带壳的海洋藻类。
A study finds that some seven million years ago, the algae had to adapt to low levels of carbon dioxide in the atmosphere. They pulled CO2 from the surrounding seas for photosynthesis as well as bicarbonate—commonly known as baking soda. The study is in the journal Nature.
一份研究发现大约700万年前，颗石藻必须适应大气中的低二氧化碳含量。他们从从周围的海洋中和碳酸氢盐中吸收二氧化碳用于光合作用。碳酸氢盐俗称小苏打。这份研究发表在《自然》杂志上。
At that same time, sea surface temperatures were dropping, plants that were more efficient at using CO2 came to predominate on land and vast glaciers began to expand on the continents—an Ice Age was underway. The low concentrations of greenhouse gases in the atmosphere were thus linked to the era’s cool climate.
同时，海洋表面温度也在下降，二氧化碳利用效率更高的植物得以主导大陆，大量的冰河开始在陆地上扩张，冰河世纪即将来临。温室气体二氧化碳在大气中的低含量也就跟冰河世纪的冰冷气候扯上了关系。
That situation is now reversed thanks mostly to fossil fuel burning. And the change is happening at least 30,000 times faster this time. In May, atmospheric concentrations of CO2 touched 400 parts-per-million for the first time in human existence. When they touch 500 ppm, the algae might no longer need the bicarbonate trick.
冰河世纪结束了，主要是由于化石燃料的燃烧。这次气候改变速度比以前快至少30000倍。五月，在人类存在时期，二氧化碳大气中含量首次变成0.04%。当二氧化碳含量变成0.05%的时候，海藻可能不再需要小苏打了。
—David Biello
