IISc researchers find evidence of shallow inland sea in south India

BENGALURU: To give a better understanding of how the earth changed from hostile living over the years, researchers from the Indian Institute of Science (IISc), Bengaluru, studied the rock deposits in southern India and have found that there was a composition of shallow, inland sea in the south Indian regions. The researchers analysed the ancient carbonate deposits in Vempalle in Andhra Pradesh and estimated the temperature and composition of shallow, inland sea that dates back to the Paleoproterozoic era. 

-Author and Professor at the Centre for Earth Sciences, IISc, Prosenjit Ghosh, said sedimentary deposits formed in the region around 1.9-2 billion years ago. These deposits are mainly stromatolites, one of the earliest fossilised life forms on the planet. 

Ghosh said this is the first such evidence found in India. Researchers are now looking to work together with China, the US and Australia where materials of similar age have been found. 

The findings provide insights into how the conditions were during that time and how it provided the right ambience for photosynthetic algae to bloom.  They said that various studies of fossils from the Palaeoproterozoic era have shown that some life might have existed even under these harsh conditions. “Large amounts of carbon dioxide in the atmosphere were absorbed by the sea and trapped as carbonates in dolomites,” said Yogaraj Banerjee, one of the authors. 

The study, published in the Chemical Geology, has been done in coordination with the University of Tennessee.  Dolomite, a direct precipitate from seawater, provides a signal not only of seawater chemistry but also of seawater temperature, said Robert Riding, Research Professor at the Department of Earth and Planetary Sciences, University of Tennessee, and co-author of the study. 

The researchers collected dolomite samples from chert – hard rocks formed by the interaction of microbes with seawater – and deposits underneath them called dolomitic lime-mud. After identifying the strata of rock where the dolomitic mud could be found the researchers then used the clumped isotope thermometry technique to analyse them. 

After two years of analysis, the team was able to figure out that the temperature of the seawater was about 20 degrees Celsius. This is in contrast to previous studies that analysed only chert samples from around the same period and had estimated that the temperature was around 50 degrees Celsius. 

The lower temperature estimate agrees more closely with the theory that the conditions were ideal for supporting lifeforms.

During the Palaeoproterozoic era, the type of water present was earlier believed to be only heavy water, containing a specific set of isotopes or forms of hydrogen. However, in the study, the team showed that light water was also present back then.