A new analysis has shown that organic molecules present on the oldest meteorite that flew from Mars to Earth were a product of interaction between water and rocks. These findings open a window into the geochemical activity in the formative years of the Red Planet. And also strike down the idea that ancient microorganisms were responsible for it.
The work, published in the journal Science, dials the clock back to 4 billion years ago when the Allan Hills 84001 meteorite – discovered in the Antarctic in 1984 – formed. The team looked at the mineralogy of this precious specimen at the nanoscale. They came to the conclusion that the organics were formed by reactions related to basalt rocks being exposed to hydrothermal water.
“Analyzing the origin of the meteorite’s minerals can serve as a window to reveal both the geochemical processes occurring early in Earth’s history and Mars’ potential for habitability,” lead author Andrew Steele, from Carnegie Institution for Science, said in a statement.
The sample shows two mechanisms at work in the formation of organic molecules. The first geochemical process is called serpentinization. It happens when circulating water interacts with igneous rocks that are rich in iron or magnesium. Serpentinization changes their chemical compositions and releases hydrogen.
The second process is called carbonization. In that case, it is slightly acidic water, rich in carbon dioxide, that interacts with rocks, leading to the formation of carbonate minerals. Based on the analysis is not clear if these two-process happened simultaneously or subsequentially. These processes have been observed on Mars before but this is the first time their combined effects have been found in the same rock.
“These kinds of non-biological, geological reactions are responsible for a pool of organic carbon compounds from which life could have evolved and represent a background signal that must be taken into consideration when searching for evidence of past life on Mars,” Steele explained.
“Furthermore, if these reactions happened on ancient Mars, they must have happened on ancient Earth, and could possibly explain the results from Saturn’s moon Enceladus as well. All that is required for this type of organic synthesis is for a brine that contains dissolved carbon dioxide to percolate through igneous rocks. The search for life on Mars is not just an attempt to answer the question ‘are we alone?’ It also relates to early Earth environments and addresses the question of ‘where did we come from?’”
The search for life on Mars continues to be fascinating. The return of samples collected by rovers in the next decade is expected to add even more to the wealth of knowledge gained by studying meteorites.