The Massive Australian Precambrian/Cambrian Impact Structure also known as MAPCIS is a proposed impact structure based upon arguments presented by Daniel P. Connelly, a pharmacist, at Geological Society of America meetings. Its center is located approximately equidistant between Uluru (Ayers Rock) and Mount Conner in Australia's Northern Territory. The structure is approximately 600 km (370 mi) in diameter. However, a hypothetical outermost ring 2,000 kilometres (1,200 mi) in diameter is claimed to be the result of undefined far field stresses. Connelly argues that the age of this hypothetical impact is approximately 545 mya which puts it just before the Cambrian explosion (542 mya) of the current Phanerozoic eon (541 mya). If confirmed as an impact structure, it would be the largest on Earth.
This proposed impact structure is listed as just a Class 3 Suspected in David Rajmon's Impact Database from the Impact Field Studies Group. Rajmon specifically noted that this proposed impact structure is highly speculative and based upon numerous unfounded interpretations, including the impact origin of the pseudotachylites and alleged ejecta deposits. It is not listed as a confirmed impact structure in the Planetary and Space Science Centre's Earth Impact Database, as only Class 0 confirmed impacts are listed on the site.