Asked by: Richard O’Neill, Glasgow
Gold has been coveted for millennia, for its beauty, malleability – and rarity. According to the World Gold Council, there are currently around 184,000 tonnes sitting in bank vaults, government reserves and personal collections. That sounds like an awful lot, until you realise that just one cubic metre of the stuff weighs over 19 tonnes. Thus, all the world’s known gold reserves could be laid out on a football pitch in a layer only a metre or so high.
But this is only the gold that has been successfully mined and documented. Estimating how much actually exists on the planet is much trickier. Chemical analysis of rock samples suggests gold makes up on average a few parts per billion of the total mass of the Earth’s crust. That means the top kilometre or so has around a million tonnes of the stuff still waiting to be dug up. Chances are it never will be, though, because most of it will be hopelessly uneconomic to extract. This was a bitter lesson learned by the brilliant German chemist Fritz Haber in the 1920s. He hoped to pay his country’s WWI reparations by chemically precipitating the gold dissolved in the world’s oceans. Haber discovered, however, that the concentrations were just too low for this to be possible.
Each litre of seawater contains just 13 billionths of a gram
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.