Ancient footprints in African volcanic ash date up to 19,100 years old.

Thousands of years ago, Ol Doinyo Lengai let forth. Thisunique Tanzanian volcano– 'Mountain of God', in the tongue of the local Masaii people – erupted on an unknown day in prehistory, sending a deluge of ash and lava down its sacred slopes.

The molten mass, carrying soil and mixing with floodwater from a nearby lake, produced a thick layer of impressionable mud that came to rest on the plains below. A short time later, before the cement-like sludge had a chance to harden, a tribe strode through the nascent mud flat, leaving a record of hundreds of fossilized human footprints that can still be seen to this day.

That hypothetical sequence of events – which might have looked something like this – is scientists' best explanation for what created the largest assemblage of ancient hominin tracks ever found in Africa, known as the Engare Sero footprints.

In a new study led by human evolutionary biologist Kevin Hatala from Chatham University in Pittsburgh, researchers examined these prehistoric impressions, to see what we could find out about the humans who made them in the mud millennia ago.

The tracks – first discovered by a local villager, before coming to the attention of researchers in 2008 – are estimated to be somewhere between 5,760 to 19,100 years old, according to previous research.

Earlier speculation that the tracks might be much older, dating to 120,000 years back – has since been constrained by newer investigations.

In any case, what makes Engare Sero special isn't so much its age; for that, the nearby Laetoli tracks, about 100 kilometres (60 miles) away, take the cake – representing what most researchers accept as the oldest footprints on the planet that can be attributed to early hominins, at around 3.7 million years old.

Rather, what sets Engare Sero apart is the vastness of its collection of preserved tracks: 408 footprints in total, left behind by a large group of individuals. Who were these ancient Africans, and what were they doing as they crossed the plains so long ago? Read the free story.