2023-10-30 18:21:47
MADRID, 30 Oct. (EUROPA PRESS) –
Most meteorites on Mars are only hundreds of millions of years old and probably come from recent volcanic events, such as those at Olympus Mons, the largest volcano in the Solar System.
Although more than 70,000 meteorites have been identified on Earth, Only about 358 of them are believed to have originated on Mars.
About three-quarters of them are classified as shergottites. They are believed to have formed in turbulent lavas from Martian volcanoes, but they have also created a kind of enigma for scientists who study the red planet.
This is because most of the surface of Mars is extraordinarily old. Using the abundance of impact craters, researchers know that most of the planet’s surface is between three and four billion years old. But when scientists determined the age of the shergottite meteorites, they got a wide range of ages, from four billion years to less than 200 million years.
This created a problem: if the surface of Mars is, on average, billions of years old, how is it possible that shergottite meteorites return with ages of only a few hundred million years? This mismatch became known as the Shergottite era paradox. A new paper published in Earth and Planetary Science Letters has solved this problem.
“One of the ideas was that Mars impacts could ‘reset’ the methods geologists use to determine the age of rocks,” he explains. it’s a statement Ben Cohen, a volcanologist at the University of Glasgow and lead author of the study.
“It used to be said that meteorites were actually four billion years old, and all the more recent numbers were because the rocks were being fully or partially reset by the heat and pressure of these impacts.”
But as more and more meteorites were studied using different techniques, most of the results obtained were curiously young, with evidence that the ages were not reset by the impact. It was evident that something was not quite right.
Historically, Martian meteorites have been dated using a variety of methods, usually giving a range of ages. One of them is known as the “argon-argon” method. In simpler terms, this measures the rate of decay of the isotope potassium-40 into argon-40. Potassium is an abundant element, making this method very versatile. It can be used to measure the age of a variety of rocks, from the eruption of Mount Vesuvius to the beginning of the Solar System itself.
This is useful for rocks that have formed on Earth, as scientists can explain extra argon contamination reaching the rocks that could skew the age. But things are a little more complicated for rocks that have been circling in space for millions of years.
“There are five potential sources of argon that shergottite meteorites may contain,” says Ben Cohen. “That compares to rocks on Earth, where there are only three.”
“The fact that these two additional sources of argon exist in the Martian samples is what makes the argon-argon system becomes complicated for shergottites.
ANALYZES IN A NUCLEAR REACTOR
By stepping back and looking at the argon-argon method with modern equipment and technology, Ben and his colleagues were able to reevaluate seven Martian meteorites. This included sticking very small pieces of them into a research-only nuclear reactor to measure argon concentrations as accurately as possible and then seeing what ages they came back at.
By looking more precisely at the chemistry of meteorites, they were able to explain the argon that the rocks gained while in space. They were also able to correct the amount of contamination that had occurred in both the Martian and Earth atmospheres.
“Once this was done, the argon-argon ages turned out to be young and fit perfectly with other methods, such as uranium-lead” explains Cohen.
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