The polar ice caps carry clues to the past. By drilling out cores of ice, scientists can can reconstruct the Earth's history. The thickness of the layers gives clues to the snowfall. Dust and chemicals in the ice keep a record of recent pollution and ancient volcanic eruption. Trapped within the ice are tiny bubbles of the ancient atmosphere.
Although solid, ice can slowly deform and flow. Vast areas of the Antarctic ice sheet are in motion, carrying thick slabs of ice from regions of high snowfall downhill towards the sea. One there, they eventually melt and are washed by the tides until giant icebergs break off, some of them as big as a small country. In mountainous regions, the snow packs harder.
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