Next month, scientists will meet in the Dordogne to mark the 150th anniversary of the discovery of the La Madeleine mammoth – an engraving on ivory that proves man had lived alongside these prehistoric creatures

Just a few weeks from now, scientists from across the globe will gather in the town of Les Eyzies in the Dordogne to commemorate one of the most important – and fortuitous – events in the study of human origins. They will congregate to mark the 150th anniversary of the discovery of the Madeleine mammoth, a small piece of ancient art that provided unequivocal proof of the deep antiquity of Homo sapiens.

The uncovering of the engraving, in 1864, was the handiwork of a joint British-French archaeological expedition and it provided the first, unambiguous evidence that human beings had once shared this planet with long-extinct animals such as the mammoth. Its discovery was also an act of extraordinary good fortune, it transpires.

"On the day the engraving was found, two of the world's leading palaeontologists happened to be at the site," says Jill Cook, an ice age art expert at the British Museum. "The piece had been fragmented and workmen carrying out the excavations would never have realised this. They would have simply dumped the bits into a bag and forgotten about them."

But by extraordinary good fortune, Edouard Lartet, who was overall director of the dig, and Hugh Falconer, a Scot who was visiting him, were present that day and realised that the bits formed a single item.

"It could so easily have been missed," says Cook. "Indeed, if science could ever be said to have been blessed with a miracle, this would be it."

The pieces found at La Madeleine, once glued together, formed a solid, two-inch-thick chunk of mammoth ivory that measured about 9in x 4in. On one side, the ivory had been carefully engraved with lines that Lartet and Falconer realised formed a picture of a mammoth. The discovery was just what Lartet and Falconer – and the excavation's backer, the British philanthropist Henry Christy – had been looking for: proof that Homo sapiens had once shared the planet with these huge, long-extinct creatures, and so must possess deep ancestry as a species.

Evidence had been mounting throughout the 18th century that our planet was incredibly old and that life had existed on it for a very long time – much, much longer than the figure of under 6,000 years that Bishop Ussher had derived in the 17th century for the date of the Earth and all living things. For example, in the 1840s, scientists had begun to realise that rock and gravel deposits found in the Alps and other regions had not been laid down by the flood but were the leftovers of the glaciers and giant icecaps that had covered much of Europe.

Today, we know these events as ice ages, but at the time the period was simply called the reindeer age, because remains of these north dwelling creatures were being found at digs in southern Europe, an indication of the intense cold that must then have enveloped the continent in the distant past, it was argued.

In addition, at several riverbank sites, including one key dig on the banks of the river Somme, in northern France, scientists had excavated human artefacts mixed with the bones of extinct animals such as the mammoth and the woolly rhino. The finds suggested that during the last ice age we might once have shared the landscape with these creatures.

But other scientists disagreed. They argued that the mixing of mammoth fossils and human tools had actually been caused by rivers and flood waters sweeping together different deposits. The mammoth bones had actually been laid down aeons before the human artefacts, they argued, but they had been mixed together by natural forces. In other words, humans did not appear on the scene until long after the mammoth had gone.

The fragment of ivory, unearthed in 1864, whose fine detail convinced palaeontologists that man had existed far earlier than was previously known. Photograph: Patrick Paillet

The excavation at La Madeleine would demolish that notion. The site at Abri de la Madeleine, in the Dordogne, a prehistoric shelter that lies under an overhanging cliff, is made up of well-preserved, distinct layers of deposits that have since been found to contain rich amounts of ancient tools, carvings and fossils of mammoths, woolly rhinos, reindeer and wolverines.

You can see a fine example of a Madeleine carving – of reindeer drawn on a bone – at the British Museum, for example. In addition, at the Natural History Museum's current Britain: One Million Years of the Human Story exhibition, two beautifully engraved bones, found at La Madeleine by Lartet and Christy, are also on display.

"The site has since lent its name to a period known as the Magdalenian era, which thrived across Europe between 12,000 and 16,000 years ago, and which we now appreciate was a time of incredible artistic creativity," says Professor Chris Stringer, curator of the Natural History Museum exhibition.

The site has certainly produced many wonders, but in terms of their sheer scientific importance none can match the splintered mammoth figurine that was spotted by Lartet and Falconer on that day in May 1864. In their hands lay fragments, freshly dug from the earth, of a beautiful engraving of a mammoth, with its distinctive domed head, that was, for good measure, made of mammoth ivory.

"You couldn't really top that in terms of proving that humans had lived at the same time as mammoths," says Stringer. "Indeed, when you examine the piece you can see details of the mammoth's anatomy that we only know about today from the frozen mammoth carcasses that we have found in Siberia."

In other words, only an artist who had shared that ancient landscape (the Madeleine mammoth was carved about 14,000 years ago) with these creatures would have been able to record one with such precision and flair – and on a piece of the animal's own ivory.

"There is no record what the two men said when they realised what they had found, or what they said to Christy when they revealed their discovery to him," adds Cook. "I suspect a lot of claret was drunk in celebration, however."

Certainly, within days, Christy and Lartet had prepared a paper announcing what their expedition had found. This was presented in Paris in June 1864, the event that will be celebrated by the scientists who will gather at Les Eyzies next month.

An illustration of a mammoth hunt, on display at the Natural History Museum. Photograph: The Natural History Museum

And there is no doubt that the Madeleine figure is a remarkable work. It has suffered over the millennia, of course – having been broken into fragments before having to endure the indignities of 19th-century conservation, which was not always of the highest standard, says Cook. Nevertheless, it is still clear that the piece was created with confidence and skill by an artist who knew mammoths and understood their behaviour.

"The large tusks are proportionate and shown in correct perspective," Cook notes in her book, Ice Age Art: Arrival of the Modern Mind (British Museum Press). "The alert eye is accurately positioned, the trunk is realistic and the lines of the jaw, as well as the dome of the skull, are appropriately massive."

The carving is an example of portable art, which contrasts with the great paintings of horses, rhinos, deer and other animals that were made in situ in caves in the Dordogne and other regions of southern Europe during the palaeolithic period. It was, nevertheless, pretty hefty and was probably kept at the site at La Madeleine, though its exact purpose remains unclear.

"One idea is that the carving was created as a sort of warning," says Cook. "Male elephants go through a period called musth, in which their testosterone levels soar and they become highly aggressive. Mammoths, which were closely related to elephants, probably went through similar bouts of behaviour. The interesting thing about the Madeleine figure is that it has been crafted to suggest movement, possibly as a reminder to fellow tribe members that these could be very dangerous animals.

"Its purpose will never be known for sure, however. On the other hand," says Cook, "there is no doubt about its impact on science and on our understanding of the deep antiquity of our origins. It was overwhelming."