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Thursday, April 20, 2006

 

Dry lake bed throws up new facts on Ganga plain

A new study suggests the Ganga plain has been agrassland with human activity for 15,000 years, and was not an uninhabitedzone of dense forests where humans didn't venture until 3,500 years ago, asgenerally believed.The study by scientists in Lucknow with collaborators in Germany andthe USis the first to reconstruct variations in monsoon and vegetationin theGanga plain in prehistoric times and connect the climatic changes to humanactivity.The scientists from the Birbal Sahni Institute of Palaeobotany and LucknowUniversity analysed pollen and chemical signatures in mud dug up from atwo-metre-deep hole in the dry lake bed of Sanai Tal, between Rae Bareli andLalganj in eastern Uttar Pradesh.Ancient pollen yields information about vegetation, while changes in themonsoon are reflected in the signatures of chemical elements buried in lakesediments."Our findings suggest that people lived in the Sanai lake region 15,000years ago," said Mohan Singh Chauhan, a scientist at Birbal Sahni Institute.Shikha Sharma, a scientist with the University of Wyoming in the US, was thelead investigator of the study published in the latest issue of the journal*Current Science*."This is bound to change ideas about human settlements in the Ganga plain,"said Indra Bir Singh, a geologist with Lucknow University who collaboratedin the study."It has been assumed that the Ganga plain was covered by dense forests thatprevented people from settling there until about 3,500 years ago, by whichtime they had developed tools to clear forests and move in," Singh said.But the Sanai lake bed tells a different story: of a seesawing monsoonaffecting vegetation and human activity.The pollen analysis shows that the Ganga plain was a savannah grassland witha few pockets of forests. The scientists also found "cultural pollen" —pollen from plants that grow at sites of human habitation."Cultural pollen is indirect evidence for human presence and we found itthroughout the 15,000-year history of Sanai Tal," Chauhan said.The lake itself formed about 12,500 years ago, during a period when themonsoon gained in strength. But the region experienced a 1,000-year spell ofdry weather between 11,500 years and 10,500 years ago. During the period,there was a clear decline in the growth of trees around the Sanai Tal, thescientists said.The levels of cultural pollen — in other words, human activity in the region— also dramatically declined during this dry spell.The studies show the largest expansion of the lake occurred between 10,000years and 5,800 years ago, a period corresponding to heavier monsoons. Earlyduring this period, Chauhan said, the region witnessed the beginnings ofagriculture.Excavations at some 9,000-year-old sites in Pratapgarh district, about 100km east of Sanai Tal, had earlier shown evidence of farming.From 5,000 years ago to the present, the levels of cultural pollen —including pollen from cultivated plants — increases significantly. Duringthis period, the Ganga plain is believed to have witnessed a largescaleinflux of people.http://www.telegraphindia.com//1060418/asp/nation/story_6113029.aspFull report at http://www.ias.ac.in/currsci/apr102006/973.pdf<http://www.telegraphindia.com//1060418/asp/nation/story_6113029.asp>RESEARCH COMMUNICATIONSCURRENT SCIENCE, VOL. 90, NO. 7, 10 APRIL 2006 973*For correspondence. (e-mail: shikha@uwyo.edu)*Correlative evidences of monsoon**variability, vegetation change and**human inhabitation in Sanai lake**deposit: Ganga Plain, India**S. Sharma**1,***, M. M. Joachimski**2**, H. J. Tobschall**2**,**I. B. Singh**3**, C. Sharma**4 **and M. S. Chauhan**4*1Department of Renewable Resources, University of Wyoming,Laramie, WY 82071, USA2Institüt für Geologie und Mineralogie, Universität Erlangen-Nürnberg,Schlossgarten-5, D-91054, Erlangen, Germany3Department of Geology, Lucknow University, Lucknow 226 007, India4Birbal Sahni Institute of Palaeobotany, 58, University Road,Lucknow 226 007, India

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