New sources are being found for coloured stones.
The three new sources were all employed as quality controllers until 2012 at the Scunthorpe site.
"As far as we can tell so far, these new sources are as accurate as the traditional ones," Professor Goodchild said.
Standards for new sources are essential, but to work properly, they must go hand in hand with requirements on plants that are already polluting.
Between them, by somewhere between 2020 and 2030, these new sources are expected almost to double U.S. domestic oil production, currently running at between six and seven million barrels a day.
Discoveries of new sources are now rare, though in the 20th century a mathematical book was found in a grave sealed before the end of the 2nd century bce, pushing back by centuries the earliest known source on the subject.
The reason is that scarcity raises prices, which spurs innovation: new sources are found, the efficiency of extraction goes up, existing supplies are used more economically, and substitutes are invented.
"We offer opinions not seen anywhere else," he says.In a world where millions of new sources are emerging on the internet, consumers are overwhelmed with information and want to be told what it all means.
With umpteen million new sources being added each year, the Internet's boisterous multimedia sibling, the World Wide Web, is now too vast an ocean of information for surfers to navigate by themselves.
At the same time, there are widespread concerns over the depletion of fossil fuel reserves and thus new sources are being explored (Cieślak and Gaj 2014).
