Kutch’s meteorite crater likely a Harappan smelting site: PRL study

Ahmedabad: A Kutch crater that was long thought to have been blasted into existence by a meteorite could actually be evidence of a civilization extracting metal.In April 2024, a picture of the ‘Luna crater’ in the Banni area of Kutch, known for its grasslands and sites such as Dhordo, was picked up as the Image of the Day on the Nasa website with a photo taken by the Landsat 8 satellite.The page described the structure as a ‘round depression in the salty plains of Kutch Basin’ and cited studies to indicate a possible meteorite impact as the reason for its formation.The primary points of consideration were the presence of ‘uncommon minerals in natural setting’ and a high concentration of a rare element, iridium.The latest study by researchers from Ahmedabad-based Physical Research Laboratory (PRL) and other institutions points to a less extraterrestrial cause — Harappan-era copper smelting — for the crater spanning 1.8km. The researchers indicate that the slag (waste after extraction of metals) could be from the Harappan period when copper was smelted at the site.The researchers also assessed earlier claims of the site being an ‘impact crater from a meteorite’ from multiple studies and concluded that the site lacks several typical signatures of such an impact.The study ‘Reevaluating the impact origin of the Luna Structure in western India using mineralogy, highly siderophile elements, and Re-Os isotopes’ is published in the journal Meteoritics & Planetary Science.The authors include Ajay Dev Asokan, Yogita Kadlag, Yash Srivastava, Khirod Kumar Das, Rumanshu Hazarika, and James M D Day from the PRL, Scripps Institution of Oceanography in the US, and Babasaheb Bhimrao Ambedkar University, Lucknow.“The circular shape; the unusual mineralogy including high-temperature mineral phases such as kirschsteinite and wustite; and the elevated abundance of highly siderophile elements (metals that dissolve in iron) have been provided as evidence in favour of an impact origin,” the study stated.Dr Yogita Kadlag, the corresponding author of the study, told TOI that the samples they recovered and analysed from the site had extremely high iron content at about 42-63% of the samples, which is much higher than the normal distribution of about 5% in the Earth’s crust.“During a meteorite impact, melting and solidification of crustal rocks occur, but the contribution from the meteorite itself generally does not exceed 1-2%,” she said. “Therefore, the unusually high iron content, along with the absence of nickel enrichment in these suspected impact rocks, provided the first clue that they are unlikely to be related to a meteorite impact.”She added, “If it has an impact origin, then enrichment of highly siderophile elements and nickel should also have been observed, which was clearly not the case.”The researchers added that high-temperature minerals such as wustite and kirschsteinite are not found in crustal rocks, which could have been brought to the surface by a major impact. Their textures, according to researchers, show strong similarities to metallurgical slags associated with smelting processes.“These two aspects prompted us to question the meteorite impact model proposed for the Luna Structure,” said Kadlag.The research also pointed to the absence of the tell-tale signs of a meteorite impact including shatter cones, shock-deformed minerals, and ultra-high-pressure phases at the site.The team then focused on the second alternative. The site is closer to a Harappan-era establishment. The age of the slags matched with the Bronze Age Harappan civilization.“We believe that these slags are related to metal smelting. However, we cannot comment specifically on the metallurgical techniques used by the Harappans,” a researcher said. “Further archaeological studies are required to address this aspect.”The site offers a rare opportunity for metallurgy and archaeology experts as it preserves evidence of ancient industrial activity in the Harappan era, and Kutch — home to the Unesco World Heritage Site Dholavira — has a large cluster of Harappan-era settlements, said experts.