Travelling seven miles over two millennia doesn’t sound like one for the record books, but that’s how long it’s taken humans to get to the bottom of the deepest oceans. The earliest divers held both their breaths and rocks to help them explore the depths, while in the intervening years we’ve developed techniques and technologies to give us some sort of control over one of the last terrestrial realms that can still be said to be unexplored. We didn’t get to the deepest point in the oceans until the 1960s, says Jeff Maynard in his superb 'The Frontier Below' (HarperCollins, £25, ISBN 9780008532727), the same decade that the Apollo missions saw men walk on the Moon.
As with the quest for the Moon, venturing into the submerged trenches between the tectonic plates of the Earth’s crust had always been both a complex and long-desired enterprise in which politics, economics and technology require their stars to align. The last of these factors has seen...