Indian geologist finds 3.5bn-year-old evidence of life in the rocks of Jharkhand

A team of Indian geologists has found our planet's earliest lifeforms that lived and died 3.5 billion years ago. Geologist Trisrota Chaudhuri of the Geological Survey of India and her team discovered the remnants of an ancient microbial community and directly dated the material for the first time. Chaudhuri said that, since well-preserved biological material and datable zircons were present in the same rock, an extremely rare occurrence, they were able to directly link the age of the rock and the evidence of life. Chaudhuri collaborated with scientists in Europe and the US for her analysis, and the study has been published in the Proceedings of the National Academy of Sciences.

Finding the earliest organisms that inhabited Earth has proved to be extremely difficult since any signs of them have changed over billions of years. But sometimes conditions lead the traces of dead microbes to be preserved inside silica. They sit there as thin layers of carbon and are not affected even when the rock is bearing the brunt of heat and pressure, causing changes in it.

The discovery was made near Jamshedpur in Jharkhand

Chaudhuri and her team made the discovery at the Singhbhum Craton, one of Earth's oldest surviving blocks of continental crust. Some rocks in Singhbhum are 3.5 billion years old. A set of black-and-white patterns was embedded in the ancient rock near Bhitardari, Jamshedpur, in the state of Jharkhand. The researchers said that these bands are remnants of microbial mats, fossilised remains in which single-celled organisms resided. "

Studying the carbon in the rock

She said that the chemical signatures preserved in this rock suggest that life forms were already using sophisticated ways of turning carbon dioxide into organic matter 3.5 billion years ago. This carbonaceous layer could have come from non-biological processes, such as volcanism, or could belong to something that lived all those years ago. To determine exactly which argument was true, they used Raman spectroscopy. They used a laser to light up the carbon, enabling them to study its structure to learn about when it formed and the alterations it went through over the years.

For it to be from an organism that was once alive, they had to establish that the carbon was indigenous to the rock and did not come from another geological event. The maximum temperature endured by the carbon was between 324 and 369 degrees Celsius, while the later veins of quartz had been heated at much higher temperatures. The cooler layers showed that the carbon was part of the original rock.

Why the discovery matters

To find the age of the material, researchers analyzed eight zircon crystals. To know when the zircon was formed, scientists looked at the ratio of uranium to lead in a zircon sample. While four crystals had undergone several changes, the other four revealed the true age, dating them back to around 3.5 billion years ago. "What we find most remarkable is that our study again confirms that primitive life thrived in a chemically extreme world 3.5 billion years ago. These microorganisms lived alongside active volcanism, in an ocean rich in iron and silica," Chaudhuri told ScienceAlert.