A team of Indian geologists has found traces of our planet’s earliest lifeforms, which 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 to 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 (PNAS).
Finding the earliest organisms that inhabited Earth has proved extremely difficult, since any signs of them have changed over billions of years. But under the right conditions, traces of dead microbes can be preserved inside silica. They sit there as thin layers of carbon and remain unaffected even when the surrounding rock bears the brunt of heat and pressure that would otherwise alter 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 village, about 20 km south of Jamshedpur, in the state of Jharkhand. The researchers said these bands are remnants of microbial mats — fossilised remains in which single-celled organisms once resided.
To determine the age of the rock and establish the biological origin of the embedded material a rock type known as chert Chaudhuri and geologist R. Mazumder collaborated with researchers from the University of California, Los Angeles; the Naturalis Biodiversity Center in Leiden, the Netherlands; and the European Institute for Marine Studies, France.
Studying The Carbon In The Rock
She said the chemical signatures preserved in this rock suggest that lifeforms 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 explanation was true, the team used Raman spectroscopy. They used a laser to illuminate the carbon, enabling them to study its structure to learn when it formed and what alterations it underwent over the years.
For it to be confirmed as coming from an organism that was once alive, they had to establish that the carbon was indigenous to the rock and had 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 determine the age of the material, researchers analysed eight zircon crystals. To find out when the zircon had formed, scientists examined the ratio of uranium to lead in each 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. Zircon crystals within the rock, dated using uranium-lead analysis, placed the rock’s age at around 3.497 billion years, which the team interpreted as the time of sediment deposition.
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“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.