Only life on Earth

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。

Early life-forms on Earth were confined to the oceans because water was the only available protection they had against ultraviolet radiation.

地球上早期的生命形式被限制在海洋里，因为水是帮助它们抵御紫外线辐射的唯一有效保护。

The finding not only presents the possibility that alternative life forms can exist, or once existed, on Earth.

这一发现不仅显示了地球上可能存在其他类型的生命，或者曾经存在过。