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》

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Nevertheless, astronomers still believed that when a comet approached the Sun—where they could study it—the Sun's intense heat would remove the corrupted surface layer, exposing the interior.

尽管如此，天文学家们仍然相信，当一颗彗星接近太阳时——这是他们可以研究它的地方——太阳的高温将会移除损坏的表层，露出内部。

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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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