Understanding this cycle is important, not only because it sustains life on Earth, but also because it is bound up with the rate of global warming.
理解这种循环很重要，不仅因为碳循环维持地球上的生命，而且因为它对于全球变暖的速度有密切关系。
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On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow, as seen in the rings visible in the cross sections of their trunks.
The near side is always facing Earth and the far side is always facing away, because the moon revolves around the Earth at the same rate that it rotates on its own axis.