双语：NASA火星探测器寻找古文明，其实不太难！

　　It could be easier to detect the signs of ancient life on Mars than it is on Earth, say scientists connected with Nasa’s next rover mission.

　　与美国宇航局下一次火星探测任务有关科学家称，在火星上发现古代生命迹象可能比在地球上更容易。

　　The six-wheeled robot is due to touch down on the Red Planet in 2021 with the specific aim of trying to identify evidence of past biology.

　　一架六轮机器人将于2021年降落在红色星球上，其具体目的是试图找到过去生物存在的证据。

　　It will be searching for clues in rocks that are perhaps 3.9 billion years old.

　　它将具有39亿年历史的岩石中寻找线索。

　　Confirming life on Earth at that age is tough enough, but Mars may have better preservation, say the researchers.

　　研究人员表示，如果在年龄如此古老的地球上的寻找生命迹象将会非常艰难，但火星的岩石可能被保存得更好。

　　It comes down to the dynamic processes on our home world that constantly churn and recycle rocks - processes that can erase life’s traces but which shut down on the Red Planet early in its history.

　　这是因为，我们的地球存在着动态过程，岩石被不断搅动和循环，这些过程可以消除生命痕迹，但红色星球在其历史早期就已经停止动态运动了。

　　"We don’t believe, for example, that Mars had plate tectonics in the way Earth has had for most of its history," said Ken Williford from Nasa’s Jet Propulsion Laboratory (JPL) in California.

　　“例如，我们不相信火星在其大部分历史中拥有如同地球板块运动的构造，”加利福尼亚州美国宇航局喷气推进实验室(JPL)的Ken Williford说。

　　"Most of Earth’s rock record has been destroyed by subduction under the ocean crust. But even the rock left at the surface is heated and squeezed in ways it might not have been on Mars.

　　“地球的大部分岩石记录已经被海洋地壳下的俯冲所摧毁。但即使是留在地表的岩石也会受到加热和挤压，这在火星上是不存在的现象。”

　　"So, paradoxically, it may well be that the older rocks on Mars are better preserved than much younger rocks on Earth," he told BBC News.

　　“因此，矛盾的是，火星上的老岩石比地球上更年轻的岩石可能保存得更好，”他告诉BBC新闻。