Published in The Hindu on July 13, 2010
When and how far did early humans venture into the cold climatic regions after they first moved out of Africa nearly 1.75 million years ago? Evidence for the earliest human occupation outside Africa has been reported from the island of Flores in the east to the Iberian Peninsula. Being restricted to latitudes not beyond 45º N, these locations were tropical, steppe, or Mediterranean settings. Even the early human presence at 52° N dating back to about 700,000 years ago in a forest-bed in Pakefield in Suffolk, U.K., was in a Mediterranean climate. A paper published online in Nature has found early humans to be more adventurous than anyone imagined. The rich haul of artefacts recovered at 52° N latitude of Happisburg, in East Anglia, U.K., is from the southern fringes of the boreal zone that is marked by a definite winter with snow. The artefacts aside, Happisburg turned out to be a treasure trove of well-preserved plant and animal fossils. These fossils strongly suggest summer temperatures between 16° and 18° C, and winter temperatures between 0 and -3° C; this means they approximated the present-day climate seen near the transition of temperate and boreal zones.
The last time a reversal in the polarity of the Earth’s magnetic field happened (when South Pole became the North Pole of today) was 780,000 years ago. The Happisburg sediments exhibit reversed polarity and this helps in setting a lower age limit for the artefacts. Palaeobotanical studies enable us to further narrow down the time of human occupation. The pollen grains and vegetation strongly suggest that human presence would have happened during the warm interglacial period around 840,000 or 950,000 years ago. The plant fossils suggest a conifer-dominated forest characterised by poor plant and animal food resources during winter. The early humans, probably the Homo antecessor, who inhabited the upper estuarine zone of River Thames would have survived the winter by turning to the water bodies. There is no evidence on how the early humans adapted themselves to the harsh winter. But survival would have been possible because they lived in a transition area between resource-poor forests and resource-rich habitats of river, marsh, and coast. Only more studies can reveal if early humans arrived during the peak warmer interglacial periods or during the colder periods.