July 8, 2010

Early Humans Migrated North Earlier Than Thought

Ancient man migrated out of Africa into northern Europe more than 800,000 years ago, far earlier than previously believed, according to a new study released Wednesday.

A collection of flint tools unearthed near Happisburgh in the eastern British county of Norfolk, where winter temperatures reach 32F degrees below zero, is from the earliest known settlement of humans, according to the landmark study published in the British journal Nature.

The discovery suggests that humans 26,000 generations ago survived climates similar to those of modern day southern Sweden, but without the benefit of clothing or fire, the scientists said.

Nearly every archaeological site discovered until now showed that human habitation across Eurasia during the Early Pleistocene period, 1.8 million to 780,000 years ago, occurred below the 45th parallel. 

This suggested a natural temperature barrier to further northward migration.  Indeed, all the previous sites were characterized as either tropical, savannah or Mediterranean in nature.

The climate boundary ran through southern France and northern Italy, Romania, southern Kazakhstan, Mongolia, and through northeastern China and the northern part of Japan's Hokkaido Island, with the only known exception being a site in southern England that humans occupied during a particularly warm interval.

But the new study challenges this 45th-parallel rule, showing for the first time that our ancestors could survive in demanding, frigid environments with only a few stone tools or weapons.

"The new flint artifacts are incredibly important," said Nick Ashton, an archaeologist from the British Museum in London and co-author of the study.

"Not only are they much earlier than other finds, but they are associated with a unique array of environmental data that gives a clear picture of the vegetation and climate," he told the AFP news agency.

Assembling the data together required several sorts of complex investigative work.  To date the tools, the scientists analyzed the magnetic data locked in different types and layers of sediment, then compared them with known changes in the direction and intensity of the Earth's magnetic fields.

But the materials did not easily allow such examination due to the lack of magnetic minerals and the amount of "noise" created by the presence of an iron-rich rock known as greigite.

So Ashton and his team also employed a technique called biostratigraphy, which examines remnant pieces of plants and animals.  By cross-referencing species that were not yet present or were already extinct, the researchers were able to confine the timeframe.

The magnetic and biological evidence "indicate a date toward the end of the Early Pleistocene," wrote the study's authors.

Reconstructing the climate and environment also meant identifying long-dead flora and fauna, including several types of seeds, pollen, pinecones, barnacles and beetles.

Weather at the site, which was located near an estuary of the River Thames that has since changed course, included average temperatures of 61 to 64 F (16 to 18 C) during the summer, and 32 to 26 F (0 - 3.0 C) during the winter months.

The area's two-legged predators likely relied on hunting animals during the winter, since edible plants would have been scarce, the scientists said.

However, these early humans would have benefited from the warming effects of the ocean, as well as access to species within the freshwater pools, salt marshes and a large tidal flood plain that contained a wide variety of grass-eating creatures.

Further excavation of the area is ongoing to solve other mysteries.

"It remains unclear whether expansion into northern latitudes with lower winder temperatures required human physical adaptation, seasonal migration or developments in technology such as hunting, clothes, the use of shelters or control of fire," the scientists said.


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