The elusive coldfinger

摘要

It was a penchant for canasta that led to the undoing of a world domination plan in an Ian Fleming novel. Fiction is simpler than reality, but simple ideas constitute powerful scientific tests. In the Earth sciences, a straightforward idea that explains some features of continents — their oceanic freeboard, their low heat flow and their gravity signature — is that they are cooler and less dense than the mantle surrounding them. A lot of a continent — hundreds of kilometres — is below the surface, so a cool continent should lower the mantle's temperature and perhaps even induce convective down- welling there. But according to Li et at (page 160 of this issue), these tell-tale features of the continental coldfinger are absent, so it doesn't dominate the world at all — or at least not continental North America, where the work was carried out.