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WHEN DID EARLY HUMANS REACH INDIA ? Stone tools suggest a million years ago , previous assumption was 0.5 million years ago. Pappu and her research team started studying the site in Tamil Nadu in 1999 (Courtesy: Shanti Pappu) EARLY humans arrived in India from Africa more than a million years ago, indicate newly discovered stone tools. The discovery overturns the earlier assumption that our ancestors reached India about half a million years ago. A research team led by Shanti Pappu of non-profit Sharma Centre for Heritage Education in Chennai discovered 3,528 stone tools at a prehistoric site in Attirampakkam in the Kortallayar river basin of Tamil Nadu. The tools fall into a class of artefacts called Acheulian tools that scientists believe were first created by Homo erectus– ancestors of modern humans– in Africa more than 1.6 million years ago. The Acheulian tools largely include handaxes and cleavers. The conclusion of Pappu 's study was earlier voiced by Robin Dennell of University of Sheffield in England in a commentary published in 2005 in the journal Nature. The Old Stone Age, or Palaeolithic Age, is divided into three periods- Lower Palaeolithic, Middle Palaeolithic and Upper Palaeolithic. Each period is characterised by typical stone tool assemblages. The Acheulian is a phase within the Lower Palaeolithic, characterised by a stone tool assemblage consisting largely of handaxes and cleavers. Acheulian populations were primarily hunters and gatherers, skilled at adapting to different WORLDLY WISE Pappu and her research team started studying the site in Tamil Nadu in 1999 (Courtesy: Shanti Pappu) environments. "We know this from fossil remains found at sites in India and world over," says Pappu. The Acheulian tools were probably used to butcher and skin animals and to exploit plant resources like roots and tubers, she adds. Dating, for the first time The archaeologists found the artefacts at a depth of one to nine metres in thick layers of clay. To date the tools, the research team analysed traces of certain elements embedded in them and by correlating the Acheulian handaxe archaeological layers excavated at the site with changes in the earth's magnetic field. Many such artefacts have been found in south India, but this is the first study that has dated the tools. The team used two dating methods, palaeomagnetic dating of the sediments that covered the Acheulian tools and cosmog~nic nuclide burial dating of the stone tools . The former is based on the principle of periodic reversal of the earth's magnetic fields over geological time periods. The palaeomagnetic measurements showed a reversed polarity, meaning the sediment samples predate the period after the last reversal of the earth 's magnetic field. "The sediments date to more than 1.07 million years," says Pappu. The burial dating technique measures isotopes of two earth metals, aluminium and beryllium, which gives the age of burial of the tool. The find ing "is one of the finest in Indian archaeology", says V N Misra, retired professor of anthropology at Deccan College in Pune. "It proves, for the first time, that early humans migrated from Africa to Tropical 52