Melting polar ice caps may have pushed some of the first ancient humans out of Europe.
New research suggests that meltwater shut down an important current bringing heat to the continent, with our early relatives unable to adapt to the chilly conditions.
Extreme climate change may have temporarily wiped humans out in Europe over a million years ago.
A sudden drop in ocean temperature would have caused the continent to become much colder, meaning that ancient humans unable to make fire or clothing wouldn’t have been able to cope and so leaving the continent empty for hundreds of thousands of years.
Professor Chris Stringer, a Natural History Museum scientist who co-authored the paper, says, ‘Such a large change in temperature would have hit these humans hard, and they didn’t quickly recover.’
‘It would have led to changes in the flora and fauna as well, which could have left these humans with limited food options. Smaller cold stages later on would have delayed any recovery further, meaning that western Europe was probably depopulated for a long period of time.’
The first humans in Europe
The earliest evidence of humans in Europe comes from Dmanisi in Georgia, where fossils and stone tools dating back around 1.8 million years were unearthed. These fossils are usually assigned to the species Homo erectus and are generally agreed to be the first evidence of humans outside Africa.
While some ancient humans continued travelling deeper into Asia, others moved west into Europe. Stone tools and fossils of ancient humans are known from Italy and southern Europe from between 1.4-1.5 million years ago, while others have been found in Spain from about 1.2 million years ago.
‘In general, the evidence for humans in Europe at this time is quite sparse and fragmentary,’ Chris explains. ‘However, it had been assumed that once humans arrived they were present more or less continuously, even if they were in small numbers.’
At the time, the climate of the Mediterranean region was generally similar to the present, but with wetter conditions that supported a mix of woodland, shrubland and wetland that provided a range of different food sources for humans and other wildlife. These periods of warmer conditions alternated with periods of relatively mild cold stages.
Until recently, it was thought that these variable conditions continued until around 900,000 years ago, when changes to climate cycles meant that Europe’s cold periods became longer and more intense. But this new study has revealed that around 1.1 million years ago there was a much harsher cold snap which had potentially fatal consequences for the humans living in Europe at the time.
The researchers used the marine cores taken from the coast of Portugal to calculate the ocean temperature at the time by examining the levels of organic molecules produced by a type of marine plankton. They also looked at pollen levels to get an idea of how the ecosystems on land were changing too.
Professor Axel Timmermann, a climate expert who co-authored the paper, says, ‘According to the sediment core data, temperatures rapidly dropped by 5-7°C in the eastern Atlantic about 1.12 million years ago.’
‘Our modelling of this event suggests that it would have resulted in a widespread and long-lasting cooling of Europe by at least 3°C. I was quite surprised to see such a massive cooling event happening so early, as we were only aware of much younger events.’
The team believe that this cooling was caused by the melting and rapid disintegration of a large ice sheet covering the Arctic, as well as parts of North America and Europe. The large amount of freshwater entering the ocean would have disrupted the Atlantic Meridional Overturning Circulation (AMOC), which brings warm water from the tropics into the north Atlantic, and weakened it by as much as 95%.
Professor Chronis Tzedakis, another co-author of the research, adds, ‘While there is a large body of evidence suggesting that glacial activity intensified around the North Sea at that time, we’re not sure why.’
‘It’s possible that this may have something to do with the particular configuration of the Earth’s orbit at that time. In any case, this is probably the first time that the glacial cycle became elongated, leading to long lasting changes in the planet’s climate.’
How did Europe change 1.1 million years ago?
As Europe became colder, the world our ancient relatives were used to would have changed dramatically.
The scientists estimated that the amount of habitable Mediterranean coastline for our ancestors would have halved, with overall plant growth dropping by a similar amount. Instead, semi-desert conditions similar to the steppes of Asia today would have become more prevalent.
The team found that pollen associated with steppe plants, such as grasses and shrubs, was about 45% more common in the sediment following the temperature change.
As these plants are not especially nutritious for humans, it would have been more difficult for them to find enough food to survive. They may also have lacked additional fat reserves meaning they were less adapted to cold conditions.
As a result, the humans who didn’t immediately die during the harsh conditions would likely have looked for more hospitable places to live outside of Europe. While the team’s research focused on Spain and Portugal, they team suspect that the inhospitable conditions might have extended further along the Mediterranean coast, and perhaps even reached southwestern Asia.
If this was the case, then Europe may have been empty of humans for around 200,000 years. When humans did return between 850,000 and 950,000 years ago, they were quite different from the people they replaced.
‘When humans came back to Europe, as evidenced by ancient footprints in Happisburgh in the UK and similar aged sites, they were tolerating colder winters than today,’ Chris says. ‘It suggests they may have adapted to become more resilient to the cold, or had developed new hunting techniques, for example, to help them survive.’
‘It’s assumed that these humans were Homo antecessor, based on the timing, but without human fossils at Happisburgh we can’t be sure.’
While the researchers’ findings represent a past instance of climate change, they also act as a warning about modern climate change. A recent paper, for instance, predicted that the melting of Greenland’s ice caps could cause the AMOC to shut down sometime this century.
Even if this prediction comes to pass, however, history will not repeat itself. The extent of climate change means that any cooling effect will be cancelled out by rising temperatures, leaving modern humans to face a very different challenge to the one their ancestors did 1.1 million years ago.
Source: NHM News
