For the first time, definitive evidence of a large impact event has been found in a martian meteorite. Zircons are geologically important minerals that can retain primary chronological information, helping geologists understand past conditions on a planetary body. However, zircons are relatively rare, and so far, scientists have studied them mainly in terrestrial crustal and lunar rocks.
The martian meteorite NWA 7034, known as “Black Beauty,” is a breccia comprised of clasts of many different types of martian crustal rocks and has been found to contain abundant grains of zircons older than 4.4 Ga (billions of years). Researchers at Australia’s Curtin University, led by Ph.D. candidate Morgan Cox, have analyzed 66 zircon grains in NWA 7034. Using a scanning electron microscope, they determined that these zircons show a variety of deformation features, including twinning that is diagnostic of impact shock pressures up to 20-30 gigapascals (one gigapascal is 9869 times the pressure of Earth’s atmosphere). These are conditions typically recorded in central peaks and peak rings of relatively large impact craters like the Chicxulub impact crater on Earth. Critically, one zircon grain was large enough for U/Pb age dating, giving an age of 4.452 Ga. This sample extends the period during which large impacts occurred on Mars by at least 30 Ma beyond previous estimations.
These newfound zircon grains show that large impacts on early Mars occurred for longer than originally thought. Large impact events have dire consequences for the planet’s habitability. Hospitable conditions could have developed on Mars by 4.2 Ga ago if there truly were no basin-forming impacts between 4.48 Ga and then. The new timeline emerging from this study suggests a later onset for this epoch, consistent with the evidence of water on the surface of Mars approximately 3.9 Ga ago, suggesting the Red Planet was hospitable to life by that time. READ MORE