Scientists have discovered never-before-seen clues about the possibility of ancient life on Mars inside a chunk of rock that was blasted off the red planet and eventually landed on Earth.
The precious Martian meteorite, which was found in Morocco in 2011, contains tiny zircon crystals that could only have been forged in a massive impact, a discovery that could rewrite the timeline of when Mars might have been habitable billions of years ago.
Videos by VICE
The newly characterized zircon grain is “the first sample of a shocked mineral interpreted to have originated from the central uplift of a complex impact structure on Mars” and provides some of “the oldest direct physical evidence of complex impact crater formation on Mars” after 4.48 billion years ago, according to a study published on Wednesday in Nature led by Morgan Cox, a PhD candidate from Curtin’s Space Science and Technology Centre in the School of Earth and Planetary Sciences.
Previous studies have examined zircon grains inside the Martian meteorite, which is officially known as Northwest Africa (NWA) 7533 and colloquially nicknamed “Black Beauty,” but Cox’s team is the first to report a clear signature of a high-intensity impact approaching the scale of the catastrophe that wiped out the dinosaurs 66 million years ago.
“The zircon represents the highest shock level reported in NWA 7034 and paired rocks and provides direct physical evidence of large impacts, some potentially life-affecting, that persisted on Mars after 4.48 billion years,” said the researchers in the study.
“During evolution of early Mars, an impact that shock-deformed zircon, if sufficiently large, may have similarly affected environmental conditions critical for the rise or maintenance of life,” the team added.
Asteroid and comet impacts in the early solar system are thought to play an important role in the origin of life on Earth, and these cataclysmic collisions would likewise have influenced any Martians that may have emerged during the red planet’s youth, when it was likely much warmer and wetter. While these impacts may play a role in nurturing life by delivering water and organic compounds to planetary surfaces, they can also instantly extinguish whole ecosystems that are unlucky enough to be located within their fallout.
For this reason, the level of asteroid bombardment on Mars is a key factor for estimating the window in which the planet may have been habitable—or, possibly, inhabited. For instance, some scientists have suggested that the frequency and intensity of Martian impacts may have eased up a bit after 4.48 billion years ago, which could have enabled habitable conditions to emerge by about 4.2 billion years ago.
The zircon grain examined by Cox and her colleagues, which was formed 4.45 billion years ago, challenges that timeline. Using advanced techniques such as scanning electron microscopy, the team identified special crystal symmetries called “shock twins” in the sample, which suggest it was formed by enormous impact pressures of at least 20 to 30 gigapascals.
“The zircon twins in NWA 7034 are well developed and are nearly identical in appearance to those reported from the three largest impact structures on Earth,” the researchers noted in the study. “The shock-twinned zircon in NWA 7034 is thus best interpreted as a remnant of shocked bedrock that originated within the central uplift (or peak ring) of a complex crater on Mars and is the most intensely shocked mineral identified thus far within the NWA 7034 meteorite suite.”
“An intense and prolonged bombardment of Mars had the potential to sterilize the planet through vaporization of liquid water and atmosphere blow off,” they added.
This new evidence of devastating impacts that occurred after 4.48 billion years ago may push the timeline of Martian habitability forward from 4.2 billion years, to somewhere between 3.9 to 3.7 billion years ago, according to the findings. This window coincides with evidence of water on Mars, which is the most important ingredient for life as we know it.
“Arguments for habitability of early Mars by 4.2 billion years that are crafted around a decline of impacts at 4.48 billion years must be reconciled with these findings, as extinction-level impact events would clearly have modified habitability conditions and hindered development of putative life,” the team concluded.
Ultimately, scientists will need to study more samples from Mars to assess its ancient habitability. So far, the only Martian rocks that scientists have been able to study are meteorites that have dropped from the sky due to pure luck, like Black Beauty. However, NASA’s Perseverance rover is currently collecting samples from an ancient Martian lakebed that will be hauled back to Earth in about a decade, if all goes to plan.
Those precious cores could finally reveal whether any microbial creatures were able to flourish during the planet’s early years, perhaps producing a brief moment in time when at least two of the solar system’s worlds nurtured young life.
