大自然能够提供人类所需要的与地球构成参照的重要实验数据，包括刚走出冰河期的世界、跌入温室气体地狱的世界、年轻的世界、古老的世界、荒芜的世界和可能充满生命的世界。
Nature has the critical experimental data that we need to finally place Earth in context, within a zoo of worlds emerging from ice ages, worlds descending into greenhouse hells, young worlds, old worlds, barren worlds, and possibly worlds teeming with life.