Richard Fisher for the BBC
At the base of the Pacific Ocean, hundreds of miles from land, there are some curious marks on the seafloor that no animal could have made. Some of them look like narrow troughs carved into the pale silt. Others could be claw marks, gouged through the ecosystems of the deep by an undersea monster.
Humanity has left many signatures on the surface of the Earth, but these long-lived features on the seafloor go largely unseen. Occasionally they are lit by the spotlights of remote submersibles, but afterwards they return to darkness. They have been there for decades. Like the footsteps and tracks that astronauts left on the Moon, they are still visible now, with nothing to wash them away.