A new study by geologists from Curtin University revealed proof of meteorite collisions on the Moon as evidence by the mineral zircon from lunar rock samples recovered during NASA's Apollo missions.

Led by microstructural geology experts Dr. Nick Timms and Professor Steven Reddy of the Western Australian School of Mines (WASM), the researchers discovered impact-related shock features in lunar zircon, which provides a new conceptual framework to trace the history and timing of meteorite impact events in our solar system.

Using microscopy facilities at Curtin, the scientists discovered the "shocking" features as they looked closely at the lunar zircon mineral grains, and finding the presence of preserved microscopic details, known as planar deformation features (PDFs), and micro-twins (impact indicators), which are only ever produced by large-scale meteorite impacts.

"This research is the first to report the presence of PDFs and micro-twins in lunar zircon, which provide unequivocal evidence of the immense pressures that occur during an impact event," Dr. Timms said.

"This research also provides a new explanation of how these features form. As shock waves pass through a rock, fractions of a second after a meteorite impact, these features form like microscopic crumple zones which are caused by directional differences in zircon's elasticity," he added.

The new approach used by the researchers allowed them to recognize impact-related features in zircon in lunar and terrestrial rocks that would otherwise be overlooked or difficult to find.

"This helps us to overcome one of the major problems with studying the impact history of the Earth, as direct evidence of impacts, such as craters, become eroded and destroyed through processes of plate tectonics, so much so that none are preserved from the earliest periods of the Earth's history," added Dr. Timms.

The oldest-known piece of lunar zircon, which was recovered from a rock sample brought back by Apollo 17 astronauts, has allowed a team of German, Australian and U.S. scientists in 2009 to give a "precise younger age limit" for the solidification of the moon's surface.

However, these lunar zircons were not studied at the time of the Apollo missions because the technology to date them did not exist, according to geologist Clive Neal of the University of Notre Dame, Indiana.

Zircon previously found in lunar rocks was dated at between 3.90 and 4.35 billion years old, the same as the oldest zircon found on Earth. But many of these lunar grains came from low-lying areas of the moon, where the crust had been resurfaced after meteorite impacts melted it.

The study was the result of a collaborative effort between the Curtin research group in Applied Geology, Dr. Nick Timms, Professor Steven Reddy, Associate Professor Alexander Nemchin, Dr. Marion Grange and Professor Bob Pidgeon, as well as Dr. Rob Hart from the Materials Characterisation Group in Curtin Applied Physics and Dr. Dave Healy at the University of Aberdeen, UK.