Mars and Earth have swapped about a billion tons of rockover the years, Carr says, and experiments show that some hitch-hiking microbes can survive the journey.
Furthermore, the designs were covered with "desert varnish", a glaze that develops on rock surfaces over thousands of years of exposure to the elements.
此外,这些设计还覆盖有“沙漠清漆”,一种在岩石表面经过数千年在这些元素暴露下而形成的釉料。
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As I said before, you can find rock art all over the world, but I'd like to focus now on the rock art of the Aboriginal people of Australia.