十万个为什么·科学阅读30篇（4）
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Why Does Ice Float—And Why Is That So Important for Life?
为什么冰能浮在水面上？这对生命有多重要？
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Ice floats because water expands when it freezes, becoming about 9% less dense than liquid water.冰能漂浮，是因为水结冰时体积膨胀，密度比液态水低约9%。
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This unusual behavior results from hydrogen bonds arranging into open hexagonal lattices as temperature drops.这种反常现象源于温度下降时氢键形成开放的六边形晶格结构。
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Most substances contract and sink when solidifying, but water’s density peaks at 4°C before decreasing.大多数物质凝固时收缩并下沉，而水在4°C时密度最大，之后随温度降低而减小。
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Floating ice forms an insulating layer that protects aquatic life beneath from complete freezing.漂浮的冰层起到隔热作用，保护下方水生生物免遭完全冻结。
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Without this property, lakes and oceans would freeze solid from the bottom up, killing most ecosystems.若无此特性，湖泊和海洋将自底部向上彻底冻结，摧毁绝大多数生态系统。
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Seasonal ice cover also regulates global climate by reflecting sunlight back into space.季节性海冰覆盖还能通过反射阳光调节全球气候。
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Polar bears, seals, and algae all depend on stable sea ice platforms for hunting and reproduction.北极熊、海豹和藻类均依赖稳定海冰平台进行捕食和繁殖。
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Glaciers move slowly because basal ice melts under pressure, lubricating their slide over bedrock.冰川缓慢移动，是因为底部冰在压力下融化，润滑其在基岩上的滑动。
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Engineers mimic ice’s low-density structure to design lightweight, strong aerogel materials.工程师模仿冰的低密度结构，设计出轻质高强的气凝胶材料。
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If water behaved like most liquids, Earth might never have developed complex multicellular life.倘若水像多数液体一样行为，地球或许永远无法演化出复杂的多细胞生命。