Nicholas Ashton, the curator of Paleolithic and Mesolithic collections at the British Museum, has been organizing “fossil road shows” in which he invites civilians to bring in any potential archaeological finds and have them identified. (One man recently showed up with a six-inch-long hippo tusk and a well-preserved ax, both found locally and both more than half a million years old.)

Having those extra eyes on the ground can make all the difference in coastal areas, Dr. Ashton said, for what the sea reveals, it tends to reclaim almost as soon. He learned this lesson firsthand.

In May 2013, shortly after the first set of storms, Dr. Ashton commissioned Dr. Bates, an old university friend, to work on Britain’s east coast in Norfolk. The beach near Happisburgh (pronounced hays-boro), a longstanding archaeological site, had suffered severe erosion. Dr. Ashton, an expert in early humans, wanted a geophysical survey to map any channels or rivers that might lie beneath about 30 feet of sediment. Some of these channels, he reckoned, might contain evidence of early humans because sources of freshwater would have been natural gathering spots.

It was on their second visit, on May 10, that Dr. Bates noticed some indentions on the otherwise flat horizons of the laminated silts recently laid bare on the beach. The humps and bumps looked familiar. He told Dr. Ashton: “They’re just like the human footprints in Borth.”

Footprints of humans and animals in Borth had been dated to about 6,000 years ago. The site in Happisburgh was 900,000 years old, a time when mammoths and hippos still roamed in these parts. No human bones or prints that old had ever been found in Britain.

Could this be possible?

A frantic race against time began. Every day, the shape of the prints would blur a little more as the coming tide eroded the contours of heels, toes and arches. A team led by Sarah Duffy from the University of York arrived to apply a technique called multi-image photogrammetry, taking about 150 digital photographs of the surface area containing the prints and feeding it into a program that created a three-dimensional model. By the time another team had come to do some laser scanning, it was too late: The prints were barely visible.