A previously unknown meteorite crater has been found while Evolution Mining – Australia’s third-largest gold-mining company – was drilling for gold near the mining town of Ora Banda in outback Western Australia. The crater is not visible from the surface, but geophysical surveys show a 3-mile-wide circular structure buried in the underground. With a diameter of 3 miles (or 5 km), the Ora Banda crater is thought to be one of the largest meteorite craters in the world.

Using modern survey techniques like electromagnetic and gravimetric mapping, a team of geologists led by Perth-based geophysicist Jayson Meyers was able to map the outer rim and central uplift of the crater. The meteorite impact pushed down the ground, but then the Earth rebounded, forming the central mountain-sized uplift.

Drilling samples also provide direct evidence for an impact. Sections of the drill core show “shatter cones”. Shatter cones are often found associated with impact craters as the shock waves caused by the impact shatter the rock in a specific, cone-shaped pattern.

Based on its levels of erosion and sediments covering the site, geologists estimate the crater could be around 100 million years old.

To cause a 3-mile crater, the asteroid would have been approximately 300-600 feet (or 100-200 m) in diameter.

A second possible impact crater with a diameter of half a mile (800 m) stretching up to 600 feet (200 m) below the surface at its deepest point, was found near Coolgardie, a town located about 60 miles south of the Ora Banda crater. With an estimated age of about 800,000 years, it is not related to the larger and much older impact.

About 200 terrestrial impact craters are currently known. Over half are located in Europe, North America and Australia. The observed distributions of crater sizes and ages have been biased by postimpact geological processes like erosion; the ages of the great majority of preserved impact structures are less than 200 million years and small structures (0–3 miles diameter) are greatly underrepresented. Erosion tends to destroy or bury craters in tectonically active areas, like near fault zones or on the seafloor, only on tectonically stable continental shields, like the Canadian-, Fennoscandian- and Australian interior, impact craters are preserved over billions of years.