A new intensive survey of the Messak Settafet escarpment, a massive outcrop of sandstone in the middle of the Saharan desert, has shown that stone tools occur "ubiquitously" across the entire landscape: averaging 75 artefacts per square metre, or 75 million per square kilometre. Researchers say the vast 'carpet' of stone-age tools -- extracted from and discarded onto the escarpment over hundreds of thousands of years -- is the earliest known example of an entire landscape being modified by hominins: the group of creatures that include us and our ancestral species. The Messak Settafet runs a total length of 350...