Just when we thought we’ve heard it all about how there could be life on Mars, or at least microfossils that could have once been alien life-forms crawling all over the Red Planet millions of years ago, another theory has surfaced.
"You've got your work cut out if you're looking at ancient sedimentary rock for microfossils here on Earth—and even more so on Mars," said Craig Marshall, an associate professor of geology who recently led a study published in Astrobiology magazine.
Earth’s tectonic collisions and realignments have stressed and pressured its rocks for 3.5 billion years, and when those rocks get buried, their temperature only increases as they sink deeper. Biological compounds look anything but biological after that long. Most of them succumb to heat and pressure after so many millennia, leaving behind carbon residue that can be seen with Raman spectroscopy, which can reveal a specimen’s cellular composition. Except spectroscopy is only part of the answer.
Astrobiologists and paleontologists often make the mistake of assuming that the general look of life and a Raman signal of carbon means life, but the presence of carbon isn’t exclusive to things that are (or were) alive. High carbon levels are present in materials that come into being through other processes, such as the stuff that spews from hydrothermal vents at the bottom of the ocean, and may look like microfossils.
Marshall believes that whether or not something microscopic and fossilized was alive at some point needs to be determined with a method that could involve instruments already planned to be on board the Mars 2020 rover. The rover could gravitate toward areas in that arid red soil that may have been once hotbeds of life and use this kind of instrumentation to figure out if that area once swarmed with micro-creatures. Enter vanadium.
"We applied a new technique called X-ray fluorescence microscopy—it looks at elemental composition," said Marshall. "Vanadium … can substitute into biological compounds. If you can't unambiguously assign if something is biology or not with morphology and Raman spectroscopy in tandem—maybe we could look for a known biological element, like vanadium.”
Vanadium is found in compounds formed from biological sources, such as crude oil, black shale, and asphalt. So if Raman spectroscopy tells you it looks like a microfossil and looks carbonaceous, the vanadium in a chlorophyll molecule from some long-dead life-form (which would have been preserved by getting intertwined with carbonaceous material) could mean the difference between alien fossils and false alarms.
NASA may not yet be aware of Marshall’s work, which was successfully tested on an Earth microfossil, but the space agency may want to pay attention if it wants to prove Mars was once teeming with alien microbes.