Minerals found in the subsurface of Mars, a zone of more than three miles below ground, make for the strongest evidence yet that the red planet may have supported life, according to research "Groundwater activity on Mars and implications for a deep biosphere," published in Nature Geoscience on January 20, 2013.
Up to half of all life on Earth consists of simple microorganisms hidden in rocks beneath the surface and for some time, scientists have suggested that the same may be true for Mars. Now this theory has been supported by new research, which suggests that the ingredients for life have been present in the Martian subsurface for much of the planet's history.
When meteorites strike the surface of Mars, they act like natural probes, bringing up rocks from far beneath the surface. Recent research has shown that many of the rocks brought up from the Martian subsurface contain clays and minerals whose chemical make-up has been altered by water, an essential element to support life. Some deep craters on Mars also acted as basins where groundwater likely emerged to produce lakes.
McLaughlin Crater, described in this study, is one such basin that contains clay and carbonate minerals formed in an ancient lake on Mars. The fluids that formed these minerals could carry clues to as to whether the subsurface contained life.
"We don't know how life on Earth formed but it is conceivable that it originated underground, protected from harsh surface conditions that existed on early Earth. Due to plate tectonics, however, the early geological record of Earth is poorly preserved so we may never know what processes led to life's origin and early evolution," said Dr Joseph Michalski, lead author and planetary geologist at the Natural History Museum in London. "Exploring these rocks on Mars, where the ancient geologic record is better preserved than on Earth, would be like finding a stack of pages that have been ripped out of Earth's geological history book. Whether the Martian geologic record contains life or not, analysis of these types of rocks would certainly teach us a tremendous amount about early chemical processes in the solar system."
Co-author Deanne Rogers, Assistant Professor in the Department of Geosciences at Stony Brook University used data from the Thermal Emission Spectrometer aboard NASA's Mars Global Surveyor and the Thermal Emission Imaging System aboard the Mars Odyssey orbiter to detect and identify minerals that proved to be consistent with a sustained aqueous environment on the floor of the McLaughlin Crater.
"Our understanding of Mars is changing very rapidly with all of the new mission data," said Professor Rogers. "There have been several recent observations and models that have pointed to the possibility of a vast store of groundwater in the Martian past, and perhaps present. So you might expect that deep basins such as McLaughlin, which intersect the upwelling groundwater table, would contain evidence of this water. And this study found that evidence."
Current exploration of Mars focuses on investigating surface processes because sedimentary rocks are most likely to provide the best chance evidence for habitability. Evidence suggests, however, that the Martian surface environment has been quite inhospitable to life for billions of years. In future missions, scientists could choose to target rocks related to the surface or subsurface, or perhaps do both by targeting areas where sedimentary rocks formed from subsurface fluids.
Michalski concludes: 'In this paper, we present a strong case for exploring the subsurface, as well as the surface. But I don't personally think we should try to drill into the subsurface to look for ancient life. Instead, we can study rocks that are naturally brought to the surface by meteor impact and search in deep basins where fluids have come to the surface.'
Co-author Professor John Parnell, geochemist at the University of Aberdeen, commented, "This research has demonstrated how studies of Earth and Mars depend on each other. It is what we have observed of microbes living below the continents and oceans of Earth. They allow us to speculate on habitats for past life on Mars, which in turn show us how life on the early Earth could have survived. We know from Earth's history that planets face traumatic conditions such as meteorite bombardment and ice ages, when the survival of life may depend on being well below ground. So it makes sense to search for evidence of life from that subsurface environment, in the geological records of both Earth and Mars. But it's one thing to do that on Earth -- we need to be clever in finding a way to do it on Mars."
Additional co-authors of the study include: Javier Caudros, Researcher, Clay Mineralogy, Earth Sciences Department, Natural History Museum, London; Paul B. Niles, Planetary Scientist, NASA Johnson Space Center; and Shawn P. Wright, Postdoctoral Fellow in Geology, Auburn University.
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