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 the stuttering evolution of subsea contraptions that originated in crude wooden diving bells, clumsy diving suits and other unwieldy paraphernalia, into 21st-century submersibles such as film director James Cameron's Deepsea Challenger, as well as the atmospheric diving suit (ADS) and the autonomous underwater vehicle (AUV). If ever technology played a critical role in our efforts to explore, it is in the underwater world.
Maynard's account is about more than exploration in the time-honoured senses of pushing the frontiers of both scientific discovery and the simple human need to satisfy our curiosity about the unknown. As Maynard says, reaching the bottom of the ocean offers tangible rewards for the many countries that have developed drones and submersibles capable of operating in such a hostile environment. The ocean economy, which he describes as "ocean-based industries combined with assets and resources provided by marine ecosystems," is set to double in size over the next decade. There is much to be gained, he concludes, from gaining technological control of the deep: "nations are realising they will soon be using AUVs to protect their underwater space in the same way they use drones to protect their airspace".
He sees it as inevitable that such machinery will be increasingly deployed for underwater military operations – especially communications via acoustic modems – which will put pressure on the natural environment. Maynard's research shows that the long-term effects of the current "cacophony" of underwater noise produced by global shipping, underwater mining and offshore windfarm construction will be "catastrophic".
And yet, our revived interest in exploring the ocean depths – it has ebbed and flowed in a manner similar to space exploration – can also be a force for good. Advances in the "armour of technology" required to explore both environments could well contribute to the long-term survival of human life on the planet.
