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.