Although we haven’t stepped foot on Mars yet, humanity have gradually come to inhabit it. Rock fragments from Mars that were expelled from their homeworld by catastrophic impacts have made their journey through the Solar System and have finally collided with Earth.
A strange pattern has surfaced as we gather these samples from our neighboring planet. The majority of the samples appear to be relatively young rocks that originated on the red planet; this is unusual considering how old the majority of the Martian surface is.
The age measurements might not be entirely accurate. Scientists aren’t quite certain in their estimates of when these rocks formed on Mars because different dating methods have produced differing results.
Now, an American-British scientific collaboration has discovered a solution to this issue. They were surprised to learn that many of these rocks are actually rather recent, dating back only a few hundred million years. This data may provide light on Mars’s geological processes and the length of time it took the meteorites to arrive.
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The study’s lead volcanologist, Ben Cohen of the University of Glasgow, adds, “We know from certain chemical characteristics that these meteorites are definitely from Mars.”
“Massive impact events have blown them off the crimson planet, leaving behind enormous craters. However, we are unsure of the precise location of the meteorites on Mars because the planet has tens of thousands of impact craters. An excellent indicator of their source crater’s age is the age of the samples.
It has been determined that over 360 meteorite samples that were discovered on Earth originated on Mars. The majority of them, or about 302 as of the time of writing, are categorized as shergottite, a metal-rich Martian rock that was formed by intense volcanic activity.
Mars’ surface is extremely cratered, leading scientists to believe that it is quite old. Volcanic flows would wipe out many of the craters if the surface was younger and renewed by volcanic activity. Thus, any rocks that are expelled from the Martian surface ought to be ancient as well.
The date of shergottite on Earth is not only made difficult by their composition, but what little we have learned about them suggests that many of them are younger than 200 million years. The shergottite age conundrum, which has been plaguing scientists for decades, is the result of this.
Explainations for this unexpectedly youthful potential varied from the hypothesis that all the younger shergottite originated from a single point of origin to the theory that the rock’s age was sort of reset by the impact event, which heated and compressed it to a certain extent. The rocks themselves provided evidence, however, which these hypotheses could not match.
Based on the radioactive potassium’s disintegration into argon, argon-argon dating is the technique used to ascertain the age of shergottite. The known ratio of argon isotopes produced by this decay rate allows scientists to date the rock sample by estimating the length of time the radioactive decay has been occurring.
The issue is that we can readily account for several sources of argon that could enter a sample on Earth. This is more complicated for shergottite, which originated on a different planet and spent, god knows how long, in space. Compared to just three Earth rocks, shergottite has five possible sources of argon.
In order to make up for this, Cohen and his associates created a technique to account for argon pollution from both space and Earth. “Once we did that, the argon-argon ages came out as being young and matched perfectly with other methods, like Uranium-Lead,” according to him.
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Seven shergottite samples were dated, yielding dates that ranged from 161 million to 540 million years ago. According to the researchers, this could be because of how often Mars is bombarded, which has shattered the planet’s older surface and exposed the younger rock underneath that has been renewed by volcanic activity. It eventually becomes more likely that the younger rock will be removed by excavation and ejection.
Mars is constantly being bombarded, and there may still be active volcanic activity there. Scientists estimate that 200 or more impacts annually produce craters larger than 4 meters in diameter. So it should come as no surprise that younger rocks are periodically sent in a direction similar to that of the Solar System toward Earth.
Earth and Planetary Science Letters has published the findings.