Scientists call such markers "proxies" for the thing they actually want to measure — in this case, the geographic extent of the ice in the past.
科学家称这种标志物为“替代品”，代表他们真正想要测量的东西——在本例中，即在过去冰的地理范围。
The national sport of Canada is ice hockey. They sometimes also call it "Canadian hockey". It is a popular game for both boys and girls all over the country.
加拿大的国家运动是冰球。有时它们也称作“加拿大曲棍球”。它是流行于全国男女老少的一项运动。
What's more, the ice doesn't quit at the level of the soil. It's also below the surface in places that do occasionally get sunlight — a kind of lunar permafrost, the scientists call it.
冰会存在于一定土层。在偶尔能照到太阳的表面下，科学家把它叫做一种月球冻土。
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