This former Homestake gold mine in the Black Hills of South Dakota is becoming a major underground research laboratory. Primarily focused on high energy physics, SURF is now also characterized by studies of underground life. The site accesses about ~170 km of mine workings, with a subset currently maintained and ventilated. Black Hills geology is extraordinarily complex, characterized by a core Precambrian granite, pegmatite, and metamorphic complex, rimmed by Paleozoic, Mesozoic, and Cenozoic sedimentary units.

Astrobiologists are participating in an underground drilling project aimed at detecting and characterizing microbial life in the subsurface. A new experiment was started near electrical and data service at the depth of 1,478 m. Here, In situ electrode-assisted cultivation of subsurface microbes is being conducted for the first time. The next phase of work at SURF will involve proposals to develop a distributed, kilometer-scale, 3D microbial observatory using select legacy holes from the surface to the 4850 level.

Sanford Underground Research Facility (SURF) - http://sanfordlab.org/

Hydrothermal vent systems are relevant to astrobiology for a number of reasons. Firstly, they provide energy to support diverse communities of organisms in one of Earth's most isolated and extreme environments. Many organisms found at hydrothermal vents have unique strategies and mechanisms for survival, and provide important clues about the adaptation and evolution of life on Earth. Some theories also suggest that hydrothermal vent systems could have been an ideal location for the origins of life on Earth. They may also serve as suitable analogs for potentially habitable environments in the ice-covered oceans of worlds like Jupiter's moon Europa or Saturn's moon Enceladus. Finally, hydrothermal vents have existed throughout the history of Earth, and likely existed on other worlds like Mars, when it was wetter and warmer. Studying the signatures of life at hydrothermal vents could help astrobiologists determine how to identify biosignatures, both in Earth's geological record and on other worlds in the Solar System where similar habitats could have existed.

Hydrothermal hot springs are found in the shallow seas off of Italy's Aeolian Islands, and they support microbial communities that can provide information about the strategies and mechanisms life uses to survive in extreme environments. Both modern and ancient rocks in these systems can also be used to understand the types of biosignatures that are left behind in hydrothermal systems.

Geochemical Society Feature Article - http://www.geochemsoc.org/publications/geochemicalnews/gn133oct07/vulcano/

The Atacama desert in South America is one of the driest locations on Earth. Certain regions of the desert contain surface sediments with incredibly low numbers of microorganisms. Life in the Atacama has adapted to harsh conditions like a severe lack of water, increased oxidation, and high salinity.

The surface environment in the Atacama is dry and contains very low numbers of microorganisms, which is a suitable place for testing life detection instruments and drills for future missions to Mars.

An integrated rover/drill is being used at sites in the Atacama Desert that are flight prototypes comparable to those planned for ExoMars and Icebreaker. It will acquire drilled cuttings and transfer to the rovers instruments. This work will test on-board autonomy and monitoring to support drilling, and demonstrate science support (operations and control) for the rover/drill/instrument operations.

Life is able to survive on Earth deep below the planet's surface. Entire ecosystems are able to thrive in the deep subsurface as long as there is access to even the smallest amount of water and nutrients. Subsurface environments can present many extreme conditions, among which are high pressures, limited nutrients, limited water, high temperatures, extreme acidity and alkalinity, metal toxicity, and radioactivity. Studying life in the deep subsurface of the Earth, and the biosignatures of such life, can also help astrobiologists understand life's past and present potential beneath the surface of other worlds.

Studying life in the 35 million-year-old Chesapeake Bay Impact Structure (CBIS) helps astrobiologists understand how life survives and evolves deep underground in impact-fractured crust. Hydrothermal environments formed by the release of energy during impact could have persisted long after the impact event itself, and biosignatures in the CBIS could help shed light on how to identify life in transient hydrothermal ecosystems in impact basins, both on Earth and beyond. Studying the modern day presence and diversity of microorganisms in CBIS sediments can also provide a view into how subsurface ecosystems recover from the large-scale shock and disruption associated with impacts.

Science article: Deep Drilling into the Chesapeake Bay Impact Structure - https://www.sciencemag.org/content/320/5884/1740.short

The Dead Sea hosts extremophile salt-loving archaea, which make unique membrane lipids that can be preserved in the rock record. The environment appears to facility lateral gene transfer between and among bacterial and archaeal salt-loving species, potentially due to the enhanced stability of environmental DNA fragments.

Extreme salt and high acidity make the Dead Sea a possible analog for Martian oceans at some time in its geologic past. Combining molecular biology, geochemistry, microbiology, and metagenomics, scientists are deciphering the microbiology, fossilization processes, and recoverable biosignatures from this mission-relevant environment.

Biofilms are particularly adept at colonizing extreme environments, from hot springs to glaciers. In Frasassi, they exist on damp walls and in the pools and streams of an underground aquifer, entirely without light and mostly without oxygen. Yet these self-contained ecosystems have found a way not just to survive, but to thrive. In fact, their presence plays a vital role in the cave system’s continuing formation. The underground environment they inhabit is a rare working model of early Earth.

Frasassi represents a “sulfur world,” an ecosystem based not on oxygen, but on sulfur as an energy source. Understanding the workings of this system offers clues to how early life evolved. Within the layers that make up a biofilm there are many different types of microbe species, each playing a different role in the community. Through genetic analyses, astrobiologists are trying to map which organisms live where in the caves and how they correspond to the geochemical environment.

Cave Microbiology
2013 BBC documentary

Hydrothermal vent systems are relevant to astrobiology for a number of reasons. Firstly, they provide energy to support diverse communities of organisms in one of Earth's most isolated and extreme environments. Many organisms found at hydrothermal vents have unique strategies and mechanisms for survival, and provide important clues about the adaptation and evolution of life on Earth. Some theories also suggest that hydrothermal vent systems could have been an ideal location for the origins of life on Earth. They may also serve as suitable analogs for potentially habitable environments in the ice-covered oceans of worlds like Jupiter's moon Europa or Saturn's moon Enceladus. Finally, hydrothermal vents have existed throughout the history of Earth, and likely existed on other worlds like Mars, when it was wetter and warmer. Studying the signatures of life at hydrothermal vents could help astrobiologists determine how to identify biosignatures, both in Earth's geological record and on other worlds in the Solar System where similar habitats could have existed.

The Gakkel Ridge, located in the Arctic Ocean between Greenland and Siberia, was explored during the Arctic Gakkel Vents Expedition (AGAVE). Two autonomous underwater robots, called Jaguar and Puma, were developed for the Astrobiology Science and Technology for Exploring Planets (ASTEP) element of the NASA Astrobiology Program. The underwater explorers demonstrated autonomous robotic operations in deep-sea vent environments. Jaguar and Puma were designed to locate hydrothermal vent sites on the seafloor of the Arctic Ocean and search for life there.

Dive and Discover, Expeditions to the Seafloor - http://www.divediscover.whoi.edu/expedition11/index.html

The Juan de Fuca Ridge is a tectonic spreading center located off the coasts of the state of Washington in the United States and the province of British Columbia in Canada. Life is able to survive on Earth deep below the planet's surface. Entire ecosystems are able to thrive in the deep subsurface as long as there is access to even the smallest amount of water and nutrients. Subsurface environments can present many extreme conditions, among which are high pressures, limited nutrients, limited water, high temperatures, extreme acidity and alkalinity, metal toxicity, and radioactivity. Studying life in the deep subsurface of the Earth, and the biosignatures of such life, can also help astrobiologists understand life's past and present potential beneath the surface of other worlds.

The Juan de Fuca Ridge provides an opportunity to study sub-sea floor microbiological communities associated with hot springs in the vicinity of an active spreading center. Here, astrobiologists study life's adaption to extremes of pressure, cold, and salinity. Studies on microbial metabolism at this site also provide insight into how scientists can use chemical and isotopic signatures to identify ancient metabolisms recorded in the rock record.

Circulation Obviation Retrofit Kit (CORK) observatories were installed in boreholes drilled into the seafloor at the Juan de Fuca Ridge. The observatories were used to sample deep subsurface oceanic basement fluids; which are heated, under pressure, and flow and percolate through layers of subseafloor rock formations. These fluids are studied for biogeochemical, microbiological and virological analysis. This extreme environment harbors a deeply buried biosphere, and could be a suitable analog for subsurface biospheres on worlds like Enceladus and Europa.

The Dynamic Earth - http://www.mnh.si.edu/earth/text/4_3_2_0.html
Places in the Sea - http://www.marine-conservation.org/media/shining_sea/place_epacific_juandefuca.htm
WHOI - Dive and Discover - http://www.divediscover.whoi.edu/expedition8/

At this acid neutralization site, effluent from the Iron Mountain mine flows into the Keswick Reservoir. The effluent has a low pH and is high in iron (Fe). Neutralization causes large amounts of ferric hydroxides to precipitate, and these support a microbial community of Fe(III)-reducing bacteria. The very high Fe, but low sulfur fluxes at the site are a possible analog for the Archean oceans on Earth prior to 2.5 billion years ago.

Geochemistry, toxicity, and sorption properties of contaminated sediments and pore waters from two reservoirs receiving acid mine drainage - http://toxics.usgs.gov/pubs/wri99-4018/Volume1/sectionD/1504_Nordstrom/pdf/1504_Nordstrom.pdf

Life is able to survive on Earth deep below the planet's surface. Entire ecosystems are able to thrive in the deep subsurface as long as there is access to even the smallest amount of water and nutrients. Subsurface environments can present many extreme conditions, among which are high pressures, limited nutrients, limited water, high temperatures, extreme acidity and alkalinity, metal toxicity, and radioactivity. Studying life in the deep subsurface of the Earth, and the biosignatures of such life, can also help astrobiologists understand life's past and present potential beneath the surface of other worlds.

If life ever existed on ancient Mars, it may have retreated to subsurface shelters when surface conditions became unfavourable. Many Martian volcanoes were built from individual flows that were emplaced through channels and lava tubes, signalling a style of volcanism analogous to Hawaiian eruptions. Such lava tubes may be one of the few places on Mars where saturation levels of moisture could have been maintained by the diffusion of geo-thermally heated groundwater. These cave systems could have also shielded ancient organisms from high UV levels. In some ways, the lava cave environment may provide an analogue to potentially habitable environments on ancient Mars.

The summit of Kilimanjaro hosts melting/subliming glaciers with stratigraphic layering, including embedded atmospheric dust, that are believed to be nearly 12,000 years old. The periglacial soils and supraglacial meltwater ponds are among the most extreme microbial habitats on Earth, as microbes eking out a living in these near-sterile environments face extreme freeze-thaw cycles, high UV flux, half an atmosphere of pressure, and extreme low organic carbon content.

These factors make Kilimanjaro an excellent Europa analog. By studying microbes found here, they will further our understanding of microbial growth boundary conditions, habitability, and preservation of organics.

Ice is retreating and thinning worldwide. Glaciers and ice fields are expected to significantly shrink within a generation, and many of the lower-altitude glaciers could disappear during the next 10-20 years. The International Panel on Climate Change (IPCC 2007) lists the Central and Southern Andes as particularly vulnerable.

Astrobiologists are working here to better understand the changes currently affecting Earth’s glacial lake ecosystems, and shed light on how life and habitats adapted and transitioned during past deglaciations on our planet. In the process, they hope to bring new insights into Mars habitability and life potential during comparable geological periods early in Mars history and later, during high-obliquity cycles when snow precipitation and glacier formation were possible. Investigating these lakes will also confront us with challenges presenting analogies to those faced by future missions to the planetary lakes and seas of Titan, thus giving us an opportunity to develop and test exploration strategies for future planetary lake landers

Planetary Lake Lander SETI - http://pll.seti.org/?page_id=5
Planetary Lake Lander Project Video Series - https://astrobiology.nasa.gov/seminars/other-seminar-series/planetary-lake-lander-project-video-series/

Ice-covered aqueous environments on Earth provide the opportunity to study organisms that survive in extreme environments where they experience low temperature and oftentimes high pressures and long periods of isolation. A select few of these sites could serve as suitable analogs for habitable environments on icy worlds with liquid water in their subsurface.

Lake Vida is located in Antarctica's Victoria Valley, which is one of the northernmost of the McMurdo Dry Valleys. The lake is covered by a permanent ice layer some 20 meters (65.6 ft) thick. Brine in the lake is also is the coldest, most stable cryo-environment known on Earth. Lake Vida brine has the highest levels of nitrous oxide (N2O) ever measured in a natural environment, and the waters of the lake have been in permanent darkness for an estimated 3000 years.

Ancient microbes discovered in bitter-cold Antarctic brine - http://phys.org/news/2012-11-hearty-bitter-cold-antarctic-brine.html

Coast Range Ophiolite Microbial Observatory (CROMO) was established in 2010 with the aim of creating a subsurface “observatory” to study serpentinite-hosted subsurface biospheres. Serpentinization is a class of water-rock reactions with the potential to generate large amounts of hydrogen and possibly hydrocarbons and organics. It can support subsurface communities over geologically-long time scales.

At CROMO, astrobiologists have established a subsurface “observatory” by drilling 8 wells into a shallowly buried, actively serpentinizing body, characterized the cores, and outfited the boreholes for a program of long-term observations and experimentations.They consider this subsurface observatory in serpentinizing terrane to be unique, and envision that the established observatory would ultimately become a resource for the broader astrobiology community, creating a central site and test bed in which to integrate a range of approaches.

Antarctica contains some of the coldest and driest environments known on Earth. The content is one of astrobiology's oldest sites of interest in the study of life in extreme environments. Antarctica has also long served as an analog for ancient Mars.

The McMurdo Dry Valleys have been used for testing life detection instruments since the early days of NASA. Although this dry and freezing environment looks lifeless, microorganisms do survive in the extreme conditions. Protected under the surface of rocks, cryptoendolithic microbial communities survive the low temperatures, scarce water availability, and high seasonal variations in solar radiation. These microorganisms have existed in this habitat for thousands of years; and have “biosignatures” that preserve and indicate traces of past biological activity. Studying these communities can help astrobiologists understand life in extreme environments and the signatures that could provide evidence for life on other worlds.

The Mid Cayman Rise is Earth’s deepest and slowest spreading mid-ocean ridge. Hydrothermal vent systems are relevant to astrobiology for a number of reasons. Firstly, they provide energy to support diverse communities of organisms in one of Earth's most isolated and extreme environments. Many organisms found at hydrothermal vents have unique strategies and mechanisms for survival, and provide important clues about the adaptation and evolution of life on Earth. Some theories also suggest that hydrothermal vent systems could have been an ideal location for the origins of life on Earth. They may also serve as suitable analogs for potentially habitable environments in the ice-covered oceans of worlds like Jupiter's moon Europa or Saturn's moon Enceladus. Finally, hydrothermal vents have existed throughout the history of Earth, and likely existed on other worlds like Mars, when it was wetter and warmer. Studying the signatures of life at hydrothermal vents could help astrobiologists determine how to identify biosignatures, both in Earth's geological record and on other worlds in the Solar System where similar habitats could have existed.

By exploring this extreme section of the Earth’s deep seafloor, research done here seeks to extend our understanding of the limits (in terms of extreme environments) to which life can exist on Earth, to understand how geologic processes might generate the prebiotic materials believed to have been an essential pre-cursor to life on Earth, and to help prepare for future efforts to explore for life on other planets.

Mid-Cayman Rise Expedition - http://www.schmidtocean.org/story/show/1507

The origins of animals has remained shrouded in mystery since the origins of paleontology, principally because of their abrupt appearance in rocks dated at around 530 Ma with little or no sign of possible antecedents in Precambrian rocks. This does not mean that older rocks are devoid of life, indeed rocks of the last half of the Ediacaran period (~580-542 Ma) are chock full of interesting but enigmatic and unmistakably non-animal forms. This location hosts the oldest known Ediacaran fossils, and thus the first solid evidence for the origin of animal life on Earth.

The fossil record provides the best evidence for the emergence of complex life and its relationship to changes in the environment. Astrobiologists are working with the fossil record of some of the oldest fossil evidence of animals and applying studies of the development of modern animals to interpret these fossils. The goal is to understand the interactions between changes in the physical environment, ecological interactions and in developmental mechanisms in evolutionary innovations leading to greater biological complexity.

http://www.flickr.com/search/groups/?q=fossil&m=pool&w=1195123%40N20&page=3
http://www.ucmp.berkeley.edu/vendian/mistaken.html

Canyon Lands National Park near Moab, Utah, is an exceptional site to study biological soil crusts (BSCs). BSCs are a complex consortia of microorganisms including cyanobacteria, algae, and fungi, and are the primary colonizers of desert soils, supplying both carbon and nitrogen to these arid-land ecosystems. As such, they may represent an analog for soil development on the early Earth. BSCs occupy an extremely nutrient-poor niche, and meet their nutrient and metal requirements by manipulating their surroundings via the production of metal-binding ligands called siderophores. The soil crusts metabolism affects the chemical composition of soil porewaters and soil solid phases; these alterations to soil metal contents may represent a biosignature for biological soil crusts that can be preserved over long time scales.

An effort to understand how microbial soil crusts obtain nutrient elements from the soil is a focus of the work done here. Samples collected here are measured for soil properties (pH, bulk density, cation exchange capacity), carbon and nitrogen content and isotopic composition, trace element composition, and basic mineralogy. Manipulation experiments were conducted to assess whether BSC metabolism is nitrogen limited, as well as experiments to determine the effects of BSC metabolism on metal concentrations in soil porewater.

The Mojave Desert is a desert which occupies a significant portion of southeastern California and smaller parts of central California; southern Nevada, southwestern Utah and northwestern Arizona in the United States. The Mojave is a desert of temperature extremes and because of that it is considered a good analog for extraterrestrial environment such as Mars.

Astrobiologists have been working with field instrumentation that will enable in-situ measurements of organics and biological material that have high potential for future flight instrumentation. These instruments provide new measurement capabilities that have been developed with the specific goal of life-detection using next generation imaging spectrometers, chromatographic, and sample extraction devices.

NAI - Jet Propulsion Laboratory, Icy Worlds 2013 Annual Report Investigation 4: Path to Flight - http://nai.nasa.gov/annual-reports/2013/jpl-icy-worlds/investigation-4-path-to-the-flight/

The Pilbara Craton is one of only two pristine ancient crust sites identified on Earth. It comprises six components:
(1) Early Archaean 3.6-2.7 Ga crust.
(2) The East Pilbara Terrane, consists of four volcano-sedimentary groups and one formation.
(3) The West Pilbara Superterrane, consists of three granite-greenstone terranes.
(4) The Kurrana Terrane, consists of two granitic supersuites and minor greenstone.
(5) The De Grey Superbasin, consists of five sedimentary basins that are filled with sedimentary and volcanic rocks.

The Pilbara Craton exposes some of the Earth's most ancient sedimentary rocks. The origin and sustenance of life on Earth strongly depends on the fact that volatile elements, H-C-O-N, were retained in sufficient abundance to sustain an ocean-atmosphere. Research here involves studing of how terrestrial planets (the inner planets closest to our Sun) form, why differences exist among the terrestrial planets, how volatiles behave deep within the Earth, and how volatiles and life influence the large and small scale composition of the near surface Earth.

ScienceDirect publication 3.43 billion-year-old stromatolite reef from the Pilbara Craton of Western Australia: Ecosystem-scale insights to early life on Earth

Originating in the Sierra de Huelva mountains of Andalusia, Spain's "red river" runs through the southwestern region of the country. For approximately five thousand years, copper, gold, silver and other minerals have been mined along the river, with dissolving iron giving it a strange reddish hue.

Extremophile aerobic bacteria in the water provide conditions similar to those found in other areas in the solar system. Jupiter's moon Europa, for example, is thought to contain an acidic ocean underneath its surface. Life in the Rio Tinto - the bacteria feed on iron and sulfide minerals in the river's subsurface rocks - make the likelihood of life on Europa all the more possible.

Research from work at Rio Tinto using a sophisticated technique that analyses the three stable isotopes of oxygen and their relationship to each other, has recently shown that the oxidation of sulfite governs the oxygen isotope composition of sulfate. This work will be of significant importance in helping to understand the conditions of the formation of ancient minerals.

An airborne remote survey of Rio Tinto has monitored the progress of the metabolic process in which iron is oxidized by bacteria. Progress has been made in linking orbital observations with those made by the MER and MSL rovers on Mars with field research at Rio Tinto, and detailed laboratory experiments that constrain the relationship between mineral combinations and their signatures advancing our ability to detect organics or “biosignature”.

Life Under a Spanish Red River, By Astrobio – Apr 10, 2003
http://www.astrobio.net/topic/origins/extreme-life/life-under-a-spanish-red-river/

Atlas Obscura – Rio Tinto (Red River)
http://www.atlasobscura.com/places/rio-tinto

SERC – Microbial Life Educational Resources – Rio Tinto
http://serc.carleton.edu/microbelife/topics/riotinto/index.html

The Norweigan archepelago of Svalbard is a remote and isolated environment filled with icy glaciers and barren, rocky landscapes deep within the Arctic circle.

Scientists with the Arctic Mars Analog Svalbard Expedition (AMASE) traveled there to test the protocols, procedures, and equipment needed to detect traces of organic chemistry and perhaps life on Mars. Instruments that are onboard NASA’s Mars Science Laboratory and will fly on ESA’s ExoMars missions were tested in Svalbard by the AMASE team. With a unique combination of volcanoes, hot springs, and permafrost, the Bockfjord Volcanic Complex on Svalbard is the only place on Earth with carbonate deposits identical to those found in the famous Martian meteorite ALH84001. What a unique opportunity to study the interaction between water, rocks, and primitive life forms in a Mars-like environment!

AMASE blog from the field http://www.nasa.gov/mission_pages/mars/news/amase/

The Cedars are located in Sonoma County, in the Central Belt Franciscan Complex. It is a serpentine mountain range with perennial mineral springs, travertine deposits and chromium ore. Serpentinization, the hydration of olivine and pyroxene minerals at moderate temperatures [100 to 300C], generates heat, hydrogen and other materials relevant to supporting and possibly originating life. Olivine and pyroxene make up > 50% of the earth's mantle. These are primordial minerals that are present on the moon, mars, meteorites, etc.

Biogeochemists and microbiologists have been studying the chemistry and bacteria in the highly alkaline (pH=10-12), highly reducing, oxygen-depleted, hydrogen-rich mineral springs and consider these springs to be a Martian analog.

Carbonates are found everywhere in Earths geologic record and their chemical and isotopic compositions have been key to discussions on the compositions of the ancient oceans, as well as the evolution of life. The abundance of Fe-carbonates, common in banded iron formations (BIFs), and the Archean sedimentary rock record, has led many scientists to use such carbonates as a proxy for surface conditions and to provide insights into seawater chemistry of the ancient Earth.

For carbonates to yield information about ancient ocean compositions, they must demonstrate to have been a direct precipitate from ocean water and not subsequently modified. One approach geochemists are taking is to test if ancient carbonates record seawater by studying the isotopic compositions of elements that usually reflect seawater compositions in carbonate minerals.

Antarctica contains some of the coldest and driest environments known on Earth. The content is one of astrobiology's oldest sites of interest in the study of life in extreme environments. Antarctica has also long served as an analog for ancient Mars.

University Valley is located in the McMurdo Dry Valleys, and contains subsurface ice-cemented ground similar to that found on areas of Mars. This site has been used to test drilling equipment that could be used to collect sub-surface samples from these regions.

About Ice Cores - National Ice Core Laboratory - http://icecores.org/icecores/drilling.shtml

West Lake Bonney is a two-and-a-half mile long, one-mile wide, 130 foot-deep lake located in Antarctica's Dry Valleys. The lake is perpetually covered with 12 to 15 feet of ice. Ice-covered aqueous environments on Earth provide the opportunity to study organisms that survive in extreme environments where they experience low temperature and oftentimes high pressures and long periods of isolation. A select few of these sites could serve as suitable analogs for habitable environments on icy worlds with liquid water in their subsurface.

Using autonomous underwater vehicles deployed down a melt hole, scientists characterize the aqueous chemistry of the lake, create high resolution 3D maps of the underwater interface between Taylor Glacier and West Lake Bonney, and create a high resolution bathymetric map of the lake floor.

ENDURANCE (Environmentally Non-Disturbing Under-ice Robotic ANtarctiC Explorer) - https://www.evl.uic.edu/endurance/endurance.html

The extreme variation in the geochemical composition of present day hydrothermal environments is likely to encompass many of those that were present on early Earth, when key metabolic processes are thought to have evolved. Yellowstone National Park harbors >12,000 geothermal features that vary widely in temperature and geochemical composition. Such environments provide a field laboratory for examining the tendency for guilds of organisms to inhabit particular ecological niches and to define the range of geochemical conditions tolerated by that functional guild (i.e., habitat range or zone of habitability).

Astrobiologists are examining the distribution and diversity of genes in YNP environments that harbor geochemical properties that are thought to be similar to those that characterize early Earth.

Yellowstone National Park Guide to Life in Extreme Heat - http://www.nps.gov/yell/learn/nature/otherlifeforms.htm
Online Guidebook: Secrets of the Springs: Astrobiology in Yellowstone National Park - http://astrobiology.com/2011/01/new-online-guidebook-secrets-of-the-springs-astrobiology-in-yellowstone-national-park.html