A breakthrough study revealed that Ice Age hunter-gatherers created cave art with their paintings, narrating their daily lives on the walls.

Decoding marks on the drawings for the first time, a team of specialists has proven that at least 20,000 years ago, people across Europe made notes about wild animals and the timings of their reproduction cycles.

Remarkably, the initial discovery that the markings on drawings could refer to a kind of lunar calendar was made not by an academic, but by London-based furniture conservator Ben Bacon who spent countless hours of his own time looking at examples of cave painting and analyzing data.

The so-called "proto-writing" system pre-dates others that are thought to have emerged during the Near Eastern Neolithic by at least 10,000 years.

Bacon said he went to academics with his theory and they listened and encouraged him to pursue it, despite him being "effectively a person off the street."

He collaborated with a team including two professors from Durham University and one from University College London to publish a paper in the Cambridge Archaeological Journal.

Cave paintings of species such as reindeer, fish, now-extinct cattle called aurochs, and bison have been found across Europe.

Archaeologists have long known that sequences of dots and other marks on the drawings had meaning, but no one could decipher them.

Bacon was keen to decode these, particularly the inclusion of a "Y" sign – formed by adding a diverging line to another – which he believed meant "giving birth."

By using the birth cycles of equivalent animals today as a reference point, the team was able to work out that the number of marks associated with Ice Age animals was a record, by lunar month, of when they were mating.

Bacon, who has an English degree but decided not to go into academia, said: "The meaning of the markings within these drawings has always intrigued me so I set about trying to decode them, using a similar approach that others took to understanding an early form of the Greek text. Using information and imagery of cave art available via the British Library and on the internet, I amassed as much data as possible and began looking for repeating patterns."

"As the study progressed, I reached out to friends and senior university academics, whose expertise was critical to proving my theory. It was surreal to sit in the British Library and slowly work out what people 20,000 years ago were saying but the hours of hard work were certainly worth it," he added.

Professors Paul Pettitt and Robert Kentridge, both of Durham University, have worked together to develop the field of visual palaeopsychology, the scientific investigation of the psychology that underpins the earliest development of human visual culture.

Professor Pettitt, of the Department of Archaeology at Durham University, said: "To say that when Ben contacted us about his discovery was exciting is an understatement. I am glad I took it seriously. This fascinating study has brought together independent and professional researchers with expertise in archaeology and visual psychology to decode information first recorded thousands of years ago. The results show Ice Age hunter-gatherers were the first to use a systematic calendar and mark to record information about major ecological events within that calendar."

"In turn, we're able to show that these people, who left a legacy of spectacular art in the caves of Lascaux and Altamira, also left a record of early timekeeping that would eventually become commonplace among our species," they added.

Kentridge, Professor of the Psychology of Vision, Durham University, said: "The implications are that Ice Age hunter-gatherers didn't simply live in their present, but recorded memories of the time when past events had occurred and used these to anticipate when similar events would occur in the future, an ability that memory researchers call mental time travel."

Also, part of the research team was Tony Freeth, an Honorary Professor at University College London, who said: "I was stunned when Ben came to me with his underlying idea that the numbers of spots or lines on the animals represented the lunar month of key events in the animals' life cycles."

The team, which also included independent researchers Dr. Azadeh Khatiri, and Clive James Palmer, a retired history teacher, hopes to do more.

Bacon said: "As we probe deeper into their world, what we are discovering is that these ancient ancestors are a lot more like us than we had previously thought – these people, separated from us by many millennia, are suddenly a lot closer."