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World’s second oldest rock is from Odisha
 The 4.2 billion-year-old zircon in the rock offers fresh clues about the earth’s origins

A rock sample recovered nearly eight years ago from Champua in Odisha’s Kendujhar district has put India at the forefront of geological research in the world. Scientists have found in the rock a grain of magmatic zircon (a mineral that contains traces of radioactive isotopes) that is an estimated 4,240 million years old — a discovery of great promise to study the earth’s early years.

Geologists from the University of Calcutta and Curtin University, Malaysia, along with researchers from the Chinese Academy of Geological Sciences, Beijing, made the discovery, which was published last week in the journal Scientific Reports.

Rajat Mazumder, geologist and one of the authors of the paper, said that the only instance of zircon older than this discovery was the one found in Jack Hill, Western Australia, which was 4,400 million years old and is the oldest known rock sample. But the zircon in this case was from metamorphosed sedimentary rock, unlike the Singhbhum one, which was formed from magma.

“Thus, the Singhbhum rock from where the zicron was recovered is the second oldest and its zircon, the oldest magmatic zircon on earth,” Dr. Mazumder said.

Along with Dr. Mazumder, Trisrota Chaudhuri, a scholar with the University of Calcutta who is also associated with the Geological Survey of India (GSI), had spent years researching the Singhbhum rocks of Odisha.

Turned to China

Dr. Mazumder and Ms. Chaudhuri studied the samples at the Geological Studies Unit of the Indian Statistical Institute, Kolkata. The isotopic analysis was a big challenge. They approached many laboratories in Australia, Canada, Germany and the US, in vain. They finally turned to China. “The machine used is called Sensitive High Resolution Ion Microprobe (SHRIMP). It is not available in India. Dr. Yusheng Wan, a Senior Researcher with the Beijing SHRIMP Center at the Chinese Academy of Geological Sciences, Beijing, agreed to analyse only four samples on a collaboration basis,” Dr. Mazumder said. The analyses confirmed the presence of two zircon grains that were 4,240 million and 4,030 million years old.

“Their study will add valuable information about the presence of water in the first few hundred million years of the Earth’s history. It will also give us clues to when plate tectonics began,” Dr. Mazumder said.