How a secret trapped in the rock for a million years was revealed and gone within a fortnight
"Diligence is the mother of good luck." So says the 16th century proverb its truth would be met with a nod of recognition for a team of scientists who discovered the Happisburgh footprints.
The small indentations locked in a sedimentary layer of estuary mud in East Anglia were huge in their significance and they form one of the headlines of the new Britain: One Million Years Of The Human Story at the Natural History Museum.
They represent a very tangible clue to the appearance of early humans on this island a million years ago, some 500,000 years earlier than the previous marker - Boxgrove man.
But, although they had survived for epochs beneath ground, they were at the mercy of the sea. They were exposed, spotted, recorded and then lost to the sea within two weeks. Spotted by luck and gone before they were even formally identified.
Fortunately, scientists had been studying the area as a rich source of finds when the footprints came to the surface.
Dr Simon Lewis, pictured below right, from Queen Mary's School of Geography in Mile End has been helping to piece together the geological puzzle surrounding the discovery which is evidence of Homo antecessor - the first known humans in northern Europe.
A co-director of the Happisburgh project, Dr Lewis said the chance of encountering footprints such as this was extremely rare - they had survived environmental change and the passage of time.
Timing was also crucial as "their location was revealed just at a moment when researchers were there to see it" during a geophysical survey. "Just two weeks later the tide would have eroded the footprints away."
The importance of the Happisburgh footprints is highlighted by the rarity of footprints surviving elsewhere. Only those at Laetoli in Tanzania at about 3.5million years and at Ileret and Koobi Fora in Kenya at about 1.5million years are older.
Speaking at the opening of the exhibition, Dr Nick Ashton, pictured below, of the British Museum said: "It did look like something unusual. As we removed any remaining beach sand and sponged off the seawater, it was clear that the hollows resembled prints, and that we needed to record the surface as quickly as possible.
"We went back a few days later and used an technique called multi-image photogrammetry which is a posh way of saying the stitching together of large range digital photos from different angles to create a 3D model of the surface.
"It was only really when you could see overhead clearly the entire surface that you could begin to pick out what are footprints and what might be unidentified. In one case you can see the heel, the toes, the arch."
While it is not possible to tell what the makers of these footprints - equivalent of Size Eight - were doing at the time, analysis has suggested that the prints were made from a mix of adults and children.
Their discovery offers researchers an insight into the migration of pre-historic people hundreds of thousands of years ago when Britain was linked by land to continental Europe.
At this time, deer, bison, mammoth, hippo and rhino grazed the river valley. The land provided a rich array of resources for the early humans with edible plant tubers, seaweed and shellfish nearby, while the grazing herds would have provided meat.
Dr Lewis's research into the geology of the site has provided information on the sediments in which the prints were found. "My role is to work out the sequence of deposits at the site and how they were laid down. This means I can provide a geological context for the archaeological evidence of human occupation at the site."
When asked whether he had a sense of the scale of the discovery on first sight, Dr Ashton said: "My scientific brain kicked in and asked 'what isn't it?'. It was only really when I got an email from Sarah Duffy [of York University] who did the overhead imaging and it was just so obvious."
But there was a long wait, running from the discovery in May to confirmation in the summer of 2013 during which time the sea had reclaimed the prize.
Dr Ashton said: "There was quite a big gap - she'd been away, she needed time to process them, then she was working on other projects but when she sent them through, there they were and there was no doubt.
"The site's importance is its rarity - it's the oldest set of footprints outside Africa - but for the public it is a more tangible link to our early human relatives in northern Europe.
"What's nice about it is that you have the larger prints probably male, and you've got smaller prints as well which are probably women and children so you've a family grouping walking on the edge of the estuary on the ancient course of the River Thames 900,000 years ago.
"Bringing all that together and seeing those footprints in the estuary mud you can really begin to picture what they were doing."
Until Sept 28, National History Museum, £9 (£4.50), nhm.ac.uk