As a group of ancient humans walked across a muddy beach in England nearly a million years ago, little did they know that one day, their footsteps would thrill modern discoverers.

The find—believed to be the oldest known human footprints found outside of Africa—wouldn't have happened without a rare combination of mud with just the right consistency, still or slow-flowing water, and a bit of perfect timing on the part of some modern humans.

"We found them by pure chance in May last year," writes Nicholas Ashton, a curator at the British Museum in London, in a blog post about the find. The footprints might help us understand how some of our early human predecessors made their way in