One-Off Zircon Find In Mars Meteorite Has Implications For Habitability

A team from Curtin University have found evidence of shock damage in the Mars meteorite NWA 7034 colloquially known as “black beauty”. The 320-gram meteorite NWA 7034 was discovered in 2013 in the Western Sahara. NWA 7034 is a breccia, mostly a collection of broken rock fragments and minerals (mainly basalt) that solidified and became a rock over time.   

Within the meteorite, a zircon crystal has been found that exhibits twinning, which is a microstructure that indicates a large impact. Previous research indicated that the heavy bombardment of Mars stopped at 4.48 billion years ago, however, the NWA 7034 meteorite is 4.45 billion years old. This indicates that the heavy bombardment of Mars continued longer than previously thought. 

“This grain is truly a one-off gift from the Red Planet. High-pressure shock deformation has not previously been found in any minerals from Black Beauty. This discovery of shock damage in a 4.45 billion-year-old Martian zircon provides new evidence of dynamic processes that affected the surface of early Mars,” said Ms Cox, the lead author of the study, and PhD candidate at Curtin University’s Space Science and Technology Centre.

The zircon shows evidence of impact pressures of 20-30 Gigapascals, which is much higher than those caused by the launch from Mars and subsequent landing on Earth, and pressures only associated with very large impacts.

The period of heavy bombardment has implications for the habitability period of Mars. Large meteor impacts can cause mass extinction events, such as the Chicxulub meteorite which caused the extinction of the dinosaurs on Earth.  

Shock twinned zircons have not been previously described from any samples of rocks from Mars. Scientists have however viewed shock twinned zircons from both Earth and the Moon. Zircon crystals from the Jack Hills in Western Australia are also the oldest terrestrial material on Earth dated at 4.4 billion years old.

“The type of shock damage in the Martian zircon involves ‘twinning’, and has been reported from all of the biggest impact sites on Earth, including the one in Mexico that killed off the Dinosaurs, as well as the Moon, but not previously from Mars,” said Ms Cox.  

It is thought that the habitability period of Mars may have begun as early as 4.2 billion years ago if heavy bombardment stopped at 4.48 billion years ago. The findings from the team at Curtin University may mean that the habitability period on Mars did not begin until later, however, this will require further studies. The warm and wet period on Mars is thought to be around 3.9-3.7 billion years ago, so this study may indicate the beginning of the habitability period lines up more closely with this time period.

“Prior studies of zircon in Martian meteorites proposed that conditions suitable for life may have existed by 4.2 billion years ago based on the absence of definitive shock damage,” said Dr Cavosie, co-author and also from Curtin University’s Space Science and Technology Centre.   

“Mars remained subject to impact bombardment after this time, on the scale known to cause mass extinctions on Earth. The zircon we describe provides evidence of such impacts, and highlights the possibility that the habitability window may have occurred later than previously thought, perhaps coinciding with evidence for liquid water on Mars by 3.9 to 3.7 billion years ago,” said Dr Cavosie.