Teeth have a hard surface layer called enamel.

牙齿有一层叫做釉质的坚硬表层。

《牛津词典》

The Arctic mammals, known as "sea unicorns" thanks to their single long tusks, also transmitted measurements for the winter layer of surface water that shields sea ice from the warmer waters below.

这种因为长着一根长牙而被称为“海洋独角兽”的北冰洋哺乳动物，同时还传输冬季海水表面的温度，这层海水将海面冰层和下面温暖的海水隔离开来。

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Surprisingly, precious metals instead appear relatively abundant on the planet's surface and in the underlying mantle layer. [Infographic: Tallest Mountain to Deepest Ocean Trench].

令人惊讶的是，在地球表面和下面的地幔层里贵金属反而比较丰富。

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The effect of these strengthened winds whipping across the sea surface is to bring deeper, more carbon-rich water up from below, thus reducing the surface layer's capacity to absorb more CO2 from the air.

ECONOMIST: Climate change

The result is that any coating, such as an antibacterial layer, would be "self-repairing" after small amounts of damage, as the molecular chains just below the damaged layer re-cover the surface.

BBC: Coating heals itself after damage

The magic, it turns out, is in that subatomic spray, as the group treated with an electron shower benefited from a polymerizing effect or, more plainly, a bonding of molecules just above the skin's surface that yielded a tough, protective nano-layer measuring between 50- to 100-billionths of a meter thick.

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