The atmosphere acts not merely as an acrobat on a tightrope pitched far from the vertical, but as an acrobat teetering between tilting and falling, and poised there for millions of years.

• 大气层的举止不仅仅像一个高空走钢丝的杂技演员，更像一个左倒右歪摇摇欲坠的杂技演员，而且几百万年来一直保持着那个姿势。