Carroll County Public Library
Like all of Mammoth Springs, the Narrow Gauge Terrace is composed of travertine, a rock made of calcium carbonate. The calcium carbonate originated in the Madison limestone layer, created when this area was once covered by the sea 320 million years ago during the Mississippian period. When marine organisms died in this seaway, their carbonate shells formed this layer.
Mammoth Springs is located 32 kilometers outside the present Yellowstone Caldera boundary at an elevation of 1,950 meters. The same hydrothermal system that fuels other Yellowstone areas fuels Narrow Gauge. When rainwater and snow pass through the underground rock, it is heated by heat from the magma. As the water circulates through the many cracks of the limestone, it dissolves some of the calcium carbonate. This dissolved calcium carbonate precipitates out at the surface and forms the travertine terraces that form very quickly causing the surface features to constantly change. While these terraces are normally chalky white in appearance, such as those seen at Canary Springs, Narrow Gauge is grey in color because it has been oxidized and weathered.
At Mammoth Narrow Gauge, we observed several types of microbes as evidenced by the green, orange, and purple colors on the calcium carbonate surface (travertine).
Purple Sulfur Bacteria
Our first observation was of purple sulfur bacteria at the hottest part of the spring. Purple sulfur bacteria are anoxygenic photosynthesizers, which means that they get energy for metabolism from light, but that they do not produce oxygen gas as a byproduct The bacteria, however, still need a chemical source of electrons.
So where does this purple sulfur bacteria obtain electrons? It uses two electrons from the hydrogen sulfide to make carbon dioxide from the dissolved calcium carbonate. As the two electrons are pulled away, elemental sulfur is left behind. Tori Hoehler suggested that these particular purple sulfur bacteria belong to the genus Chromatium.
Unknown Green Substance
The green filamentous substance seen near the vent at Mammoth Narrow Gauge is likely another type of microbe. It could be an anoxygenic photosynthesizer.
Farther down the slope, is a darker green substance that could be bacteria or algae. Further experiments would be needed for us to know for sure, but reflectance spectral readings show two absorptions characteristic of photosynthesizing organisms (yellow/orange and deep red wavelengths). These data suggest it is either a cyanobacteria or algae.
PhormidiumThe orange bacteria growing at Mammoth Narrow Gauge is most likely Phormidium, although further testing would be required in the lab before we could say this with certainty. Phormidium is an oxygenic, phototrophic cyanobacterium. Phormidium usually lies in flat, slimy mats of tangled filaments and this is evident at Mammoth Narrow Gauge. The filaments themselves can be long and cylindrical or they may be curved.
The chart below shows spectral data of three surfaces taken at Narrow Gauge.
The microorganisms that use hydrogen sulfide and combine it with oxygen from the atmosphere producing sulfuric acid via the equation:
H2S + 2O2 → H2SO4
The calcium carbonate acts as a buffer to the sulfuric acid, so the acid does not have a chance to erode the rocks. Rather the system is actually a little alkaline. Measured pH values at Narrow Gage were 7.48. An analogy to this reaction is Tums to stomach acid. The white material seen that covers the majority of the region is travertine precipitated out by the water in the hot spring.
The temperatures are low enough and the pH is not extreme, but the hydrogen sulfide limits the photosynthetic organisms from growing due to their dislike of sulfur.
Life on Earth — and the conditional limits of life - can be used as a guage for the search for life on other planets. Elements of Mammoth Hot Springs-Narrow Gauge offer biomarkers that can be used in the search in a planet or moon’s past, present, and future. If the spectral fingerprints of the organisms found in the Narrow Gauge region were located on another planet, these would be sites for further exploration for life. Likewise, if a surface provided the spectral signature of limestone or travertine, it would be of interest because the conditions for life (liquid water) might occur in this location.
In search for life on other planets, scientists use spectroscopy, and temperature readings, among other techniques. Using the spectroscopy reading obtained at Narrow Gauge if the reflective light came back where the red and deep red are low readings (absorbed) and the infrared readings were high (reflected) — primary indications of photosynthesizing organisms - then a search of that planet or moon could be warranted. A search for a pH that was slightly alkaline and evidence of temperature that were in the range of 70ºC would also be viable for life of anoxygenic activity.
Scientists believe that Venus had some of the same chemical composition as Earth, but due to its location in the habitable zone, it is too close to the Sun and it's surface is too hot for life as we know it due to the extreme greenhouse effect.
Mars may also have had physical and chemical environments appropriate for survival of microbes similar to those we examined. Mars is located on the edge of the habitable zone, but models suggest it had the appropriate amount of light and heat at one time. Mars also had the volcanic activity that made chemical activity and a thicker, protective atmosphere a possibility early in its life.
If the theories on Europa are correct, and indeed Europa has a liquid water ocean underneath the outer layer of ice, then there may be life forms on Europa. There may be sufficient heat to drive volcanic activity at the seafloor, providing the renewable chemical energy necessary for life forms, similar to life of the vents at the mid-ocean ridges in Earth's oceans.
Earth's Extremophiles home page