The story of an ancient Martian meteorite

Some new analyses were made on a sample of Martian rock collected in Antarctica 30 years ago by some meteorite hunters. Investigations revealed an accurate recording of the climatic conditions of the red planet millions of years ago, probably when the water flowed on its surface and any possible form of life would find the best conditions to develop.
A study published last week in the online edition of Proceedings of the National Academy of Science by a research team consisting of scientists from the University of California, NASA and the Smithsonian Institution, reports the results of an accurate measurement of the composition of an ancient meteorite fell to Earth from Mars.


Credit: NASA

“The minerals contained within the meteorite are like a snapshot of ancient chemistry of the planet and interactions occurred between water and atmosphere,” says Robina Shaheen, lead author of the study.
The rock in question does not look good, has a shape similar to a potato, but its history, since about 13,000 years ago fell to Earth, it is really very exciting. Identified with the ‘name’ ALH84001 is the oldest Martian meteorite in our possession, a piece of solidified magma from a volcano spit out millions of years ago. After the expulsion of the material, once solidified, some liquid, water in all probability, was filtered through the pores of the rock depositing globules of carbonates and other minerals.
The carbonates vary slightly depending on the source from which their atoms of carbon and oxygen are. Both carbon and oxygen exist in various forms, most versions of ‘heavy’ and ‘lighter’, or isotopes. The presence of different isotopes in different quantities characterizing the rock, it is a kind of chemical fingerprint, that careful analysis and accurate measurements can reveal.
The Martian atmosphere is composed primarily of carbon dioxide, but also contains ozone. The balance of oxygen isotopes in ozone is really strange, with enrichment of heavy isotopes that occurs through a chemical-physical phenomenon described for the first time by a co-author of the study, Mark Thiemens, professor of chemistry at the UC San Diego, and his colleagues 25 years ago.
“When ozone reacts with carbon dioxide in the atmosphere, it moves the strangeness isotopic to new molecules that are formed,” added Shaheen, who has studied the phenomenon of oxygen isotope exchange in the course of his higher studies at the University Heidelberg. When the carbon dioxide reacts with water to form carbonates, the isotopic signature is retained.
The degree of isotopic oddity in carbonates reflects how much water and how much ozone were present at the time of their formation. And it is as if it were at the same time a ‘picture’ of the atmosphere of 3.9 million years ago.


Credit: NASA

“We have also carried out a measurement of carbon isotopes on the same sample. The mix of carbon isotopes present in the meteorite suggests that different minerals have had different origins, “adds Shaheen. “We tell the story of the chemical and isotopic composition of carbon dioxide in the Martian atmosphere.”

ALH84001 shows the presence of tiny tubes carbonate that some scientists saw as potential evidence of microbial life, even if the biological origin for these structures was discarded.
The carbonates may in fact be deposited by life forms that eliminate then the minerals waste to build their skeletons, but that this is not the case of measured minerals. “The carbonate that we observe is not of biological origin,” adds Shaheen. “The isotopes of oxygen that reveals tell us that this is the abiotic carbonate.”
By measuring the isotopes in different ways, chemists have found carbonates depleted in carbon-13 and oxygen-18 enriched. This indicates that the atmosphere of Mars at the time of formation of the rock, a period of great shelling, had much less carbon-13 than it contains today.
The change in the relative abundances of isotopes of carbon and oxygen may have occurred due to a large loss of the Martian atmosphere. Thicker atmosphere would probably have been necessary because the liquid water could flow on the cold surface of the planet.
“We now have a much deeper and more specific knowledge in the system primordial oxygen and water in the solar system,” says Thiemens. “The question that remains is when the planets, Earth and Mars, have ‘taken’ the water, and, in the case of Mars, where it ended up. We have made great progress, but to unravel the mysteries, they still remain very deep. “

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