The fresh dating analysis of the artifacts reveals the earliest known presence of hominins in Europe, said Roman Garba, an archaeologist at the Czech Academy of Sciences in Prague. The first humans to inhabit Europe made their way from east to west, the report also suggested.

Initial dating of the Korolevo archaeological site, discovered in the 1970s, suggested it had been used for more than 800,000 years. Archaeologists have recovered 90,000 stone tools from the site, which lies close to Ukraine’s southwestern border with Hungary and Romania.

To determine the ages of the stone tools in the lowermost archaeological layer more accurately, the team used a relatively new dating method that involved analyzing radioactive particles inside mineral grains that were produced by cosmic rays — charged particles that travel through space and rain down on Earth.

“It’s like a cosmic clock that unleashes human history,” said Garba, lead author of the study published Wednesday in the journal Nature.

The shower of radiation as cosmic rays interact with the atmosphere can penetrate rock, creating cosmogenic nuclides, or isotopes. Scientists measure the rate of decay of these nuclides to determine how long the previously exposed rock has been shielded from cosmogenic nuclides once buried below Earth’s surface where the isotopes can’t form.

Garba‘s colleagues measured two nuclides, aluminum-26 and beryllium-10, found in quartz grains from seven pebbles discovered in the same layer as the stone tools. Using two methods of calculation, the researchers determined they were 1.4 million years old.

“It’s a very complicated to process the samples,” Garba said. “You need two to three months of everyday work to grind, clean and separate the sample.”

Early hominins in Europe

No human fossils have been found at the open-air site — the exposed conditions make it harder for fossils to be preserved. The soil is also acidic, which can accelerate decomposition of artifacts, Garba said.

It’s not clear what species of early human would have occupied the site at that time, but the study suggested it would have been Homo erectus. Scientists believe the extinct species to be the first hominin to have left Africa and walk with a fully upright gait.

The earliest human fossils unearthed in Europe are from the Atapuerca site in Spain and date back 1.1 million years, according to the study. In Georgia, human fossils found near Dmanisi are thought to be 1.8 million years old.

The now securely dated stone stools from the Korolevo site fill in “a gap in early hominin presence in Europe in both time and space,” said Briana Pobiner, a paleoanthropologist at the Smithsonian National Museum of Natural History in Washington, DC, who wasn’t involved in the research.

The finding suggests that at least one spread of hominins into Europe was from east to west — and that hominins could inhabit higher latitudes of northern Europe before they colonized southern Europe. “Of course, we can’t know if this was a temporary incursion into this area, or a more permanent migration, without more data from more sites,” she said.

“Thankfully hominins left their calling cards — stone tools, and sometimes butchered animal bones — scattered across the landscape as solid evidence of their presence.”

The study team also looked at the climate and habitat of the area over the past 2 million years. The researchers found that a warmer, interglacial period, when temperatures would have been warmer than the present day, coincided with the age of the stone tools. Garba said pollen data suggested a forest ecosystem.

Korolevo would have been appealing to ancient humans because it’s near the Tisza River, which leads to the Danube, and there was a readily available source of hard rock to knap stone tools, Garba said.

Garba and his colleagues said they hope to continue their investigation of Korolevo.

However, Russia’s war in Ukraine has made it difficult to excavate and access artifacts from the site, he added.