Rock paintings in the Sahara indicate that horses and chariots were used to traverse the desert and that by 300-200 B.C., there were trade routes across the Sahara.
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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BLACK ROCK CITY, Nevada — It's hot in the desert, but not too hot to set something on fire.