According to the prevailing view, Homo erectus, an ancestor of Homo sapiens, lacked the intellectual and technological sophistication to have achieved controlled use of fire; that had to wait for the emergence of H. sapiens 40,000 years ago. However, recent evidence seriously undermines this view. At two sites in Kenya, many small, lens-shaped patches of discolored earth were uncovered along with bones and stone tools of H. erectus. Analysis showed that the patches, which, like the tools and bones, dated from 1.6 million years ago, were almost certainly the result of deliberately built fires, since those fires were evidently much hotter than typical naturally occurring bush fires. The size of the patches rules out lightning strikes, which could have explained the fires' high temperatures. Furthermore, the fires were fed by a mixture of grasses and woods that strongly suggests deliberately collected fuel. In addition, many of H. erectus' tools were made of basalt or quartz, stones which, when exposed to the intense heat near a campfire, form characteristic dimples on their surface. A recent study found that such dimples never appear on tools dating earlier than 1.6 million years ago but do consistently appear on later tools.