Published in The Hindu on July 8, 2010
How far north did early humans who migrated out of Africa some 1.75 million years ago venture? Moving towards the polar region meant encountering colder climates, and early humans were not equipped to live in such hostile climate.
All evidence of their dispersal from Africa has been restricted to tropical, savannah and Mediterranean regions not beyond 45 degree N latitude. According to a report in Nature published in 2005, early humans had indeed ventured beyond 45 degree N latitude some 7,00,000 years ago and reached Pakefield, Suffolk in the U.K that lies at 52 degree N latitude. But that was when Suffolk still had a balmy Mediterranean climate.
A report published today (July 8) in Nature has for the first time found evidence of human occupation in the boreal zone more than 7,80,000 years ago.
Boreal zone is marked by a definite winter with snow and a short summer that is generally hot. The artefacts were recovered from Happisburg that lies on the northeast coast of Norfolk, U.K. Like Suffolk, Happisburg is also at 52 degree N latitude.
About 80 artefacts, predominantly large flakes, up to 145 mm size with sharp cutting edges have been recovered from the Early and Middle Pleistocene sediments — fluvial gravels and estuarine sands. The flakes have undergone little abrasion implying the deposition at the site of human inhabitation with little transportation by the river.
Artefacts are just one of the many treasures recovered. The sediments contain well preserved plant and animal remains. These remains are indicative of a forest-fringed estuary. According to the authors, geological evidence indicates that human occupation was in the upper estuarine zone of the River Thames. That would mean that the River Thames had flowed into the sea about 150 km north of its current estuary.
Among the plant remains recovered from the sediments are pollens, seeds, pine-cones, and wood. The animal remains include foraminifera, marine molluscs, barnacles, beetles and vertebrates. Reconstructing the paleoenvironment and paleoclimate has thus become quite easy, thanks to the plethora of plant/animal remains.
The plant remains indicate “regional conifer-dominated forest with deciduous elements forming a minor component,” the authors note. There are remains that are indicative of local grasslands as well. The animal remains such as beetles point to a large, slow-moving river, while the marine molluscs, barnacles and foraminifera reflect a proximity to the estuary and salt marsh.
Reconstruction of the paleoclimate using the plant/animal remains suggests a mean summer temperature between 16 degree C and 18 degree C, and mean winter temperature between 0 degree C and minus 3 degree C.
These summer and winter temperatures are what one may expect to see in the southern fringes of a boreal zone. “These temperature estimates … are analogous to the situation that exists in southern Scandinavia today near the transition between the temperate and boreal vegetation zones,” the authors state.
Evidence from vegetation suggests an interglacial period with human occupation happening during the later part of a warm interglacial period some 8,40,000 to 9,50,000 years ago.
Unfortunately, the excavation sites have not provided any clues to the ways in which early humans survived in such cold climate during winter.
Cold climate is not the only challenge they would have faced. Vegetation of northern Europe during the interglacial periods was marked by seasonal plant resources.
The coniferous forests, in particular, are characterised by low usable biomass and poor edible plant resources during winter. Even animals would have been more dispersed during winter, thus making food availability a great challenge.
So how did these early humans survive the cold winters?
According to the authors, there is evidence that early humans who lived in Happisburg were in a transition area (ecotone) between resource-poor forests and resource-rich habitats including large tidal river, salt marsh and coast.
The only way early humans could have survived during winter was by turning to the river and sea for food.
Till date very little information was available that reflected the way early humans adapted and survived in the new climatic zones after migrating out of Africa. This study provides some information, though sketchy.
Along with the 2005 study, the latest paper strongly indicates that places in the U.K., particularly those around the River Thames and east coast bordering the North Sea Basin, are the ideal locations to look for more artefacts used by early humans.