A scar on the subcontinent
In the Baran district of Rajasthan, an otherwise flat expanse of Neoproterozoic sedimentary rock is interrupted by a circular structure 3.5 kilometers (2.2 miles) wide. This is the Ramgarh Crater, a feature first documented by geologists in 1869. For over a century, its origin was a subject of debate, with theories ranging from tectonic uplift to volcanic activity. The structure is within the Vindhyan Supergroup, a thick sequence of ancient sedimentary rocks. The crater itself is defined by a raised rim that rises about 200 meters (656 feet) above the surrounding plains, creating a distinct and visible ring.
The confirmation of Ramgarh as an impact structure is relatively recent, solidifying its place as one of three such confirmed sites in India. The structure's apparent diameter is a topic of ongoing research, with some studies suggesting the full extent of the disturbed area could be as wide as 10 kilometers. This would classify it as a complex crater, distinct from a simple bowl-shaped depression. Its official recognition as a National Geological Monument is its scientific value.
Evidence of impact
The definitive proof of an extraterrestrial origin comes from the rocks themselves. Geologists have identified microscopic shock-metamorphic features, such as planar deformation features (PDFs) in quartz grains. These tiny, parallel glass layers within the crystal structure can only be formed by the extreme pressures—exceeding 30-50 Gigapascals—of a high-velocity impact. Diaplectic glass and impact spherules, tiny beads of molten rock ejected during the impact, have also been found, further supporting the conclusion.
While the hook's 600-million-year age is a popular estimate, scientific estimates vary. Some studies, based on fossils found in post-impact sediments, suggest a much younger age of less than 165 million years, placing the event in the Mesozoic Era. Regardless of the precise date, the extreme age and subsequent erosion explain the absence of any meteorite fragments. Concentrations of elements common in meteorites, such as iron, nickel, and cobalt, have been detected in the crater's soil, giving chemical clues to the long-vanished impactor. Near the center of the crater is the Bhand Devra Temple, a 10th-century structure dedicated to the Hindu god Shiva.