Mars analog studies in Yellowstone

I recently returned from a week in Yellowstone, studying hot springs as an analog of possible environments on Mars and the early Earth.  To the casual eye, hot springs look devoid of life, but really they are teeming ecosystems of thermophilic bacteria.  Phylogenetic studies suggest these organisms are closely related to the earliest life on Earth; and Mars is known to have had extensive volcanism in its past (perhaps persisting to the present day?), including the largest volcano in the solar system, Olympus Mons.  If life ever existed on Mars, we might find evidence around ancient thermal vents.

High temperature pool ( > 90 deg C), a biofilm coats the interior
 surface, despite the near boiling temperature.

The problem is, would we know what to look for?  And if we found anything, could we be absolutely sure it was once living?  Evidence for the earliest life on Earth consists of microscopic fossils found in the Apex chert, roughly 3.5 billion years old.  However, the biogenicity of these structures is a subject of scientific debate.  Sure, the shapes resemble contemporary bacteria... but morphology alone is an insufficient biosignature.  Our understanding of the processes that lead to preservation of microstructures is incomplete. Hence, studies in contemporary mineralizing environments can lead to insight that will help distinguish abiotic pseudofossils from bona fide microfossils.

Outflow channel from the spring, all the white is silica,
all the colours are bacterial communities.

For several days, I stared at scenes like this, particularly interested in the white film of silica developing over the orange "bubblemat" -- or Phormidium.  The water from the hot spring carries dissolved silica; as the water evaporates, the silica is left behind, forming new layers of rock.  Anything present can become encased, leaving fossil traces behind.

Phormidium, or bubblemat

Phormidium is a type of cyanobacteria, responsible for the oxygenation of our atmosphere.  It grows in thick microbial mats, held together by extracellular polymeric substances (EPS) secreted by the bacteria.  The products of its respiration become trapped as air bubbles within the mat.  A thin layer of heated water flows over the surface of the mat, but the air bubbles can force part of the mat to crest the water level, initiating silica deposition.

Silica layer, at 45x magnification

I have a microscope attachment for my camera/phone, and was able to snap a few images while still in the field.  I set the lens on a mostly dry, smooth white surface of silica, and was pleasantly surprised to find filaments and air bubbles -- capturing the initial stages of microfossil preservation.


Hopefully, studies like this will help inform our understanding of the earliest life on Earth, and our search for life on Mars.

What can astrobiologists study here on Earth?

The emerging science of astrobiology seems to be lacking its primary object of study.  It seems a little premature to talk about the scientific study of aliens, when we haven't found any yet, and can hardly be considered a space-faring species ourselves.  Despite a name hinting of "space life," the scope of astrobiology includes more than just extraterrestrials.  It is the study of life within a universal context, and Earth is indeed part of the universe.  Earth-based life is the only form of life we currently know of, and in order to make predictions about the potential for life elsewhere, astrobiologists study this data point of one.  Especially...

Extremophiles -- organisms that live in extreme environments, like hot springs or dry Antarctic valleys.  (although.. the name 'extremophile' highlights our bias, as a hot spring environment can hardly be considered extreme to the organisms dwelling there.)  By studying life that thrives in environments normally considered hostile, scientists have expanded our awareness of where we might find life.  Extremes of temperature (both hot and cold), pressure, salinity, acidity, radiation... life on Earth can cope with a wide variety of conditions.  The most extreme survivors tend to be bacteria, but tardigrades are remarkable little animals that have even survived exposure to outer space.  Some extremophiles live in environments similar to what can be found in locations on Mars.  This raises the possibility that if life evolved on an ancient, wetter and warmer Mars, it might still exist there, thriving in a vast ocean of subsurface ice.

Biosignatures -- What constitutes evidence of life?  Before we can find proof of life on other planets, we need to know what we're looking for.  Most of the life on Earth, for most of its history, has been microbial.  From this, we can assume there will be more single-celled life in the universe, making detection somewhat more difficult.  Even the evidence for the earliest life on Earth is still debated, because microbes don't leave obvious bones in the ground.  Microfossil structures have that resemble contemporary bacteria have been found in sedimentary deposits dating back 3.5 billion years; but morphology is not a sufficient indicator of biogenicity.  Processes leading to the preservation of structures on the microscopic scale are not well understood, and what looks like an ancient cyanobacteria could be an abiotic artifact.  Even if Mars is dead now, it might have once harbored life.  To plan future missions and prevent overstating any evidence, astrobiologists attempt to define what makes for clear indicators of past life.

The Origins of Life -- one of the greatest ponderables of all time!  Science has yet to advance a complete theory regarding the origins of life on Earth.  The theory of evolution covers the speciation of life once it has developed, but does not address the question of life's origins.  Darwin wrote to a colleague about the possibility of life forming in a "warm little pond" initiating speculation about the primordial soup, and prebiotic chemists have since tried to recreate the recipe, without success.  The most famous experiment occurred in the 1950's, when Stanley Miller was able to synthesize some of the building blocks of life, including amino acids, from simple molecular precursors.  Currently, the RNA World hypothesis seems the main contender for the origins of life, positing simple life forms of ribonucleic acid, before the development of proteins and DNA (deoxyribonucleic acid).  An understanding of the conditions necessary for the origins of life on Earth can help guide the search for extraterrestrial life, by predicting where the transition from chemistry to biology might also have occurred.

NASA defines astrobiology as "the study of the origins, evolution, distribution, and future of life in the universe."  It is the study of the extent of life in the universe, which includes life on Earth.  Indeed, the study of Earth-based life forms the foundation of how to look for alien life, even if we have yet to find any.

Is there life on Mars?

Mars, the Red Planet, has inspired endless fascination and over forty exploratory missions (even if most have failed to reach their destination).  From Giovanni Schiaparelli's early maps of Martian canali -- interpreted by Percival Lowell as a global network of channels built by extraterrestrials -- to H.G. Wells' War of the Worlds, in which the denizens of a dying Mars invade Earth, mankind has imagined life on one of our closest celestial neighbors.


The Viking missions in the mid-1970s carried four life detection experiments to Mars, to look for signs of bacteria in Martian soil.  One of the tests reported evidence of metabolic activity, but none of the other tests could confirm; most discouraging, a GC-MS analysis found no evidence of organic compounds.  Scientific consensus deemed the seeming metabolic activity a false positive, a result of highly reactive chemicals in the soil, and Mars a lifeless planet.

Or is it?

Interest in the possibility of extraterrestrial life on Mars has been growing, especially since the unambiguous detection of water -- potentially in large amounts -- existing just beneath the surface.  Water is required for all life on Earth, and one primary strategy in the search for extraterrestrial life is 'Follow the Water.'

Satellite images revealed what appear to be water carved gullies, but debate circled around the age of these features.  Four billion years ago, Mars was wet, covered with oceans.  At roughly half the size of Earth, Mars cooled much more quickly and was not able to sustain a thick atmosphere.  The atmosphere of Mars today is too thin for liquid water to persist, any water would sublimate directly from a solid to a gas and likely escape into space.

In 2008, a robotic arm on the Phoenix lander scraped away a small area of soil and found ice.  There could well be oceans of permafrost hiding beneath a dusty red veneer, and deep subsurface aquifers with liquid water heated by geothermal processes, that occasionally bubble to the surface as geysers.  The question now is not whether water exists on Mars, but how much?

Some scientists speculate there is greater biomass existing within the Earth than on its surface.  Even in mine shafts carved a mile deep, there is life.  Bacteria buried in the rock, living in slow motion, with high heat and punishing pressures, extracting energy from chemicals normally considered poisonous.

Given what we know, it seems reasonable to suspect that if life ever managed to become established on Mars, it probably still exists there.  Conditions on Mars are not so different from what certain extremophiles here on Earth tolerate.  I imagine the first mission to drill into the surface will find a thriving Martian community of microorganisms, protected from the harsh UV conditions by a meter or two of rock.  Perhaps not the aliens promised by science fiction, but still infinitely fascinating.

The Phoenix lander also detected a high concentration of perchlorates in the Martian soil.  Recent studies with Earth soil suggest the levels of perchlorate present in Martian soil would break down any organic material under the conditions of the GC-MS experiment performed by the Viking lander.  Maybe... we did detect actually life back in the 70's, and just didn't recognize it.