Europe's first humans, a population of the archaic human species Homo erectus, were probably wiped out by an "extreme cooling event" about 1.1 million years ago, a new study finds.
The previously unknown temperature downturn coincides with what's known about human habitation of the continent, the researchers suggest. Fossils and stone tools show that Homo erectus arrived in Europe from Asia between 1.8 million and 1.4 million years ago, previous research has found, but they seem to have died out throughout Europe about 1.1 million years ago.
The next evidence of archaic humans in Europe is from about 900,000 years ago — possibly after a later and more robust species, Homo antecessor, arrived there from Africa or Asia.
"There's an apparent gap of 200,000 years," study senior author Chronis Tzedakis, a paleoclimatologist at University College London, told Live Science. This gap occurs at the same time as the newfound cooling phase, which suggests that the cold drove or wiped out any archaic humans, according to the new study, published Aug. 10 in the journal Science.
Related: Modern humans arose after 2 distinct groups in Africa mated over tens of thousands of years
Ocean evidence
The researchers found evidence for the cooling in cores of marine sediment sampled from the ocean floor off the coast of Portugal. Their analysis of elemental isotopes in the remains of marine plankton from both the ocean surface and the ocean floor, along with an analysis of pollen grains from land-based vegetation, showed an abrupt cooling about 1.15 million years ago.
Tzedakis said the water temperature near Lisbon — which is now around 70 degrees Fahrenheit (21 degrees Celsius), on average — fell to around 43 F (6 C), while Europe's landmass underwent a similar cold phase, which may have caused its northern ice sheets to advance southward.
The researchers also determined that there had been a sustained influx of cold water starting about 1.13 million years ago, which they've interpreted as meltwater from the disintegration of Europe's ice sheets as the continent warmed.
Our planet had gone through numerous cold and warm phases, and conventional timelines suggested an ice age peaked about 900,000 years ago, Tzedakis said. Although there have been suggestions of an even earlier cold period about 1.1 million years ago, there was no hard evidence of it before now, he said.
The main reason for the cooling seems to have been astronomical: Jupiter's gravitational influence meant that Earth's orbit at that time was roughly circular around the sun — a circumstance associated with other cooling phases in our planet's climate, Tzedakis said.
The period was also marked by a significant drop in the level of the greenhouse gas carbon dioxide in Earth's atmosphere, but whether that was the cause of the cooling or a consequence of it is not known, he said.
Intense cold
The new research also provides a detailed reconstruction, conducted by study co-author Axel Timmermann, a climate scientist at the Institute for Basic Science in South Korea, revealing that the extreme cooling would have made Europe too cold for archaic humans.
The cold would have made it harder for them to find food, as fewer plants and the animals that ate them would have survived. Moreover, archaic humans themselves weren't suited for the cold.
The authors wrote that the worsening environment "would have challenged small hunter-gatherer bands, compounded by the likelihood that early hominins lacked sufficient fat insulation and the means to make fire, effective clothing, or shelters, leading to much-lower population resilience," the authors wrote in the study.
Paleoanthropologist Michael Petraglia, director of the Australian Centre for Human Evolution at Griffith University in Brisbane, said the new study "made good sense."
"The environmental, fossil and archaeological evidence are in good agreement for regional abandonment, and perhaps even the extinction of early [human] populations," he told Live Science in an email.
Petraglia was not involved in the research, but he noted its relevance to the modern study of climate change.
"This is a story of how climatic variability had profound effects on hominin populations in the past, with implications for all of humanity today who face extreme weather events and changes in ecosystems," he said.
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