Life in Extreme Heat - National Park ...
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
T H E RMOP H ILE S
Thermophiles, or heat-loving microscopic organisms, are nourished by the extreme habitat at hydrothermal
features in Yellowstone National Park. They also color hydrothermal features shown here at Clepsydra Geyser.
Life in Extreme Heat
The hydrothermal features of Yellowstone are enough to blister your skin. Some create layers that
magnificent evidence of Earth’s volcanic activity. look like molten wax on the surface of steaming
Amazingly, they are also habitats in which micro- alkaline pools. Still others, apparent to us through
scopic organisms called thermophiles—“thermo” for the odors they create, exist only in murky, sulfuric
heat, “phile” for lover—survive and thrive. caldrons that stink worse than rotten eggs.
Grand Prismatic Spring at Midway Geyser Basin Today, many scientists study Yellowstone’s ther-
is an outstanding example of this dual characteristic. mophiles. Some of these microbes are similar to the
Visitors marvel at its size and brilliant colors. The
boardwalk crosses a vast habitat for thermophiles.
Nourished by energy and chemical building blocks Words to Know
available in the hot springs, microbes construct Extremophile: A microorganism living in extreme
vividly colored communities. Living with these conditions such as heat and acid, that cannot survive
without these conditions.
microscopic life forms are larger examples of life in
extreme environments, such as mites, flies, spiders, Thermophile: Heat-loving extremophile.
and plants. Microorganism: Single- or multi-celled organism of
microscopic or submicroscopic size. Also called a microbe.
For thousands of years, people have likely won-
Microbes in Yellowstone: In addition to the thermophilic
dered about these extreme habitats. The color of
microorganisms, millions of other microbes thrive in
Yellowstone’s superheated environments certainly Yellowstone’s soils, streams, rivers, lakes, vegetation, and
caused geologist Walter Harvey Weed to pause, think, animals. Some of them are discussed in other chapters of
and even question scientists who preceded him. In this book.
1889, he (Weed, 1889) wrote: Bacteria (Bacterium): Single-celled microorganisms
without nuclei, varying in shape, metabolism, and ability
There is good reason to believe that the existence
to move.
of algae of other colors, particularly the pink, yel-
Archaea (Archaeon): Single-celled microorganisms
low and red forms so common in the Yellowstone without nuclei and with membranes different from
waters, have been overlooked or mistaken for Bacteria. Once thought to be Bacteria.
deposits of purely mineral matter. Viruses: Non-living parasitic microorganisms consisting of
However, he could not have imagined what a a piece of DNA or RNA coated by protein.
fantastic world exists in these waters of brimstone. Eukarya (Eukaryote): Single- or multi-celled organisms
Species, unseen to the human eye, thrive in waters whose cells contain a distinct membrane-bound nucleus.
as acidic as the liquid in your car battery and hot
Life in Extreme Heat 139
T H E RMOP H I LE S
Thermophiles in the Tree of Life
Bacteria Archaea Eukarya
Green
nonsulfur Crenarchaeota Myxomycota
bacteria
Euryarchaeota Entamoebae Animalia
Mitochondrian Fungi
Gram-
positive Thaumarchaeota
Proteobacteria bacteria
Plantae
Chloroblast
Ciliates
Cyanobacteria Korarchaeota Nanoarchaeota
Flavobacteria Flagellates
Thermotoga Trichomonads
Thermodesulfobacterium Microsporidia
Aquifex
Diplomonads
DRAWING BY MARY ANN FRANKE
Yellowstone’s hot springs contain branch of microorganisms not known hot environments on the young Earth.
species from the circled groups on this until the 1970s—the Archaea. Relevance to Yellowstone
Tree of Life. Jack Farmer conceived of Dr. Carl Woese first proposed this “tree” Among the earliest organisms to
this version of the tree of life, which first in the 1970s. He also proposed the new evolve on Earth were microorganisms
appeared in GSA Today, July 2000 (used branch, Archaea, which includes many whose descendants are found today
with permission). microorganisms formerly considered in extreme high-temperature, and in
In the last few decades, microbial Bacteria. The ancestor of the Bacteria, some cases acidic, environments, such
research has led to a revised tree of Archaea, and Eukarya is inferred to be as those in Yellowstone. Their history
life, far different from the one taught where the blue, red, and green lines exhibits principles of ecology and ways
before. The new tree combines animal, connect. Organisms that branch closest in which geologic processes might have
plant, and fungi in one branch. The to this ancestor are hyperthermophiles, influenced biological evolution.
other two branches consist solely of which thrive in water above 176°F
microorganisms, including an entire (80°C), indicating life may have arisen in
first life forms capable of photosynthesis—the process Regardless of scientific advances, visitors and
of using sunlight to convert water and carbon diox- explorers in Yellowstone can still relate to something
ide to oxygen, sugars, and other by-products. These else Weed (Weed, 1889) wrote about Yellowstone,
life forms, called Cyanobacteria, began to create an more than a century ago:
atmosphere that would eventually support human life. The vegetation of the acid waters is seldom a
Cyanobacteria are found in some of the colorful mats conspicuous feature of the springs. But in the
and streamers of Yellowstone’s hot springs. alkaline waters that characterize the geyser
basins, and in the carbonated, calcareous waters
About Microbes of the Mammoth Hot Springs, the case is other-
Other life forms—the Archaea—predated wise, and the red and yellow tinges of the algae
Cyanobacteria and other photosynthesizers. Archaea combine with the weird whiteness of the sinter
can live in the hottest, most acidic conditions in and the varied blue and green of the hot water
Yellowstone; their relatives are considered among the to form a scene that is, without doubt, one of
very earliest life forms on Earth. the most beautiful as well as one of the strangest
Yellowstone’s thermophiles and their environments sights in the world.
provide a living laboratory for scientists, who continue
to explore these extraordinary organisms. Researchers
know that many mysteries of Yellowstone’s extreme
environments remain to be revealed.
140 Yellowstone Resources and Issues Handbook, 2022
T H E RMOP H ILE S
National Academy of Sciences of the United States of
More Information America. 106 (13): 5213.
American Society for Microbiology: www.microbeworld.org Reysenbach, A.L., and Shock, E. L. 2002 . Merging Genomes
Allen, E. T., Arthur L. Day, and H.E. Merwin. 1935. Hot with Geochemistry in Hydrothermal Ecosystems.
springs of the Yellowstone National Park. [Washington]: Science. 296: 1077-1082.
Carnegie institution of Washington. Sheehan, K.B. et al. 2005. Seen and unseen: discovering the
Brock, T.D. 1994. Life at High Temperatures. Yellowstone microbes of Yellowstone. Guilford, Conn: Falcon.
Association/Mammoth, WY. Snyder, J.C. et al. 2013. Functional interplay between a
Brock, Thomas D. 1995. The road to Yellowstone and be- virus and the ESCRT machinery in Archaea. Proceedings
yond. Annual Review of Microbiology. 49 of the National Academy of Sciences. 110 (26)
Dyer, B.D. 2003. A field guide to bacteria. Ithaca, NY: 10783-10787.
Cornell University Press. Spear, J. R. et. al. 2005. Hydrogen and bioenergetics in the
Franke, M.A, et al 2013. Genetic Diversity in Yellowstone Yellowstone geothermal ecosystem. Proceedings of the
Lake: The Hot and Cold Spots. Yellowstone Science. 21 National Academy of Sciences. 102 (7) 2555-2560.
(1): 6-22. Steunou, A.S., et al. 2008. Regulation of nif gene expression
Fouke. B.W. 2011. Hot-spring Systems Geobiology: abi- and the energetics of N2 fixation over the diel cycle in a
otic and biotic influences on travertine formation at hot spring microbial mat. ISME Journal. (4):364-78.
Mammoth Hot Springs, Yellowstone National Park, Takacs-Vesbach, C., et al. 2013. Metagenome sequence
USA. Sedimentology. 58: 170-219. analysis of filamentous microbial communities obtained
Hamilton, T.L. et al. 2012. Environmental constraints defin- from geochemically distinct geothermal channels reveals
ing the distribution, composition, and evolution of specialization of three aquificales lineages. Frontiers
chlorophototrophs in thermal features of Yellowstone Research Foundation.
National Park. Geobiology. (10) 3: 236-249. Thermal Biology Institute of Montana State University: www.
Inskeep, W.P. , et al. 2013. The YNP metagenome project: tbi.montana.edu
environmental parameters responsible for microbial Ward, D.M., Castenholz, D.W., and Miller, S.R. 2012.
distribution in Yellowstone. Frontiers in Microbiology. Cyanobacteria in Geothermal Habitats. In Brian A.
00067. Whitton, ed. Ecology of cyanobacteria II: their diversity
Klatt, C.G., et al. 2011. Community ecology of hot spring in space and time. Dordrecht: Springer.
cyanobacterial mats: predominant populations and their Weed, W. H. (1889). The vegetation of hot springs. The
functional potential. ISME Journal. 5(8): 1262–1278. American Naturalist. 23(269), 394-400.
Marquez, L. et al. 2007. A virus in a fungus in a plant: 3-way
symbiosis required for thermal tolerance. Science 315
(5811): 513–515. Reviewers
Qin, J., C.R. Lehr, C. Yuan, X. C. Le, T. R. McDermott, and B. Dr. Eric Boyd, Montana State University Department of
P. Rosen. Biotransformation of arsenic by a Yellowstone Microbiology and Immunology
thermoacidophilic eukaryotic alga. Proceedings of the Dr. Erin White, Park Hydrologist
Annie Carlson, Research Permit Coordinator
Life in Extreme Heat 141
T H E RMOP H I LE S
The travertine terraces in Mammoth Hot Springs host thermophilic Cyanobacteria.
Thermophilic Bacteria when compounds like hydrogen or sulfur react with
The word “Bacteria” is often associated with disease, oxygen. This energy is then used to convert carbon
but only a few kinds of Bacteria cause problems for dioxide into biomass (chemosynthesis). For example,
humans. The other thousands of Bacteria, although Thermus sp. may also be able to oxidize arsenic into a
all simple organisms, play a complex role in Earth’s less toxic form.
ecosystems. In fact, Cyanobacteria were responsible Individual Bacteria may be rod or sphere shaped,
for the oxygenation of our atmosphere. They were but they often join end to end to form long strands
the first photosynthesizers, converting light energy called filaments. These strands help bind thermo-
into oxygen more than 2.4 billion years ago. Without philic mats, forming a vast community or mini-
Bacteria, in particular Cyanobacteria, humans would ecosystem. Other groups of Bacteria form layered
not be here. structures resembling tiny towers, which can trap
While some Bacteria perform photosynthesis, sand and other organic materials.
others depend on chemical energy that is released
Thermophilic Bacteria in Yellowstone National Park
Name pH and Temperature Description Location
Cyanobacteria pH 6–9 Color: dark brown mats • Mammoth Hot Springs
Calothrix 30–45°C (86–113°F) Metabolism: photosynthesis by day; • Upper, Midway, and
fermentation by night Lower geyser basins
Phormidium pH 6–8 Color: orange mats • Mammoth Hot Springs
35–57°C (95–135°F) Metabolism: photosynthesis • Upper, Midway, and
Lower geyser basins
Oscillatoria pH 6–8 Color: orange mats • Mammoth Hot Springs
36–45°C (96–113°F) Metabolism: photosynthesis; oscillating moves • Chocolate Pots
it closer to or away from light sources.
Synechococcus pH 7–9 Color: green mats • Mammoth Hot Springs
52–74°C (126–165°F) Metabolism: photosynthesis by day; • Upper, Midway, and
fermentation by night Lower geyser basins
Green Sulfur pH 6–9 Color: dense, dark green mats • Mammoth Hot springs
Chlorobium 32–52°C (90–126°F) Metabolism: anoxygenic photosynthesis— • Calcite Springs
produces sulfate and sulfur, not oxygen.
Green non- pH 7–9 Color: green mats • Mammoth Hot Springs
sulfur 35–85°C (95–185°F) Metabolism: anoxygenic photosynthesis—use • Upper, Midway, and
Chloroflexus organic compounds during photosynthesis. Lower geyser basins
Aquifex pH 3–5.5 Color: yellow and white streamers • Norris Geyser Basin
Hydrogeno 55–72°C (131–162°F) Metabolism: uses hydrogen, hydrogen sulfide • Amphitheater Springs
baculum and carbon dioxide as energy sources; can use
arsenic in place of hydrogen sulfide.
Aquifex pH 5–9 Color: bright red or orange streamers; • Lower Geyser Basin
Thermocrinis 40–79°C (104–174°F) contains carotenoid pigments that act as
sunscreen.
142 Yellowstone Resources and Issues Handbook, 2022
T H E RMOP H ILE S
Archaea are the most extreme of all extremophiles, and some scientists think they have not changed much from
their ancestors. Grand Prismatic Spring at Midway Geyser Basin contains archaea.
Thermophilic Archaea features of Norris Geyser Basin and in the muddy
Archaea are the most extreme of all extremo- roiling springs of the Mud Volcano area.
philes—some kinds live in the frigid environments Whenever you see a hot, muddy, acidic spring, you
of Antarctica; others live in the boiling acidic springs are probably seeing the results of a thriving com-
of Yellowstone. These single-celled organisms have munity of archaeal cells called Sulfolobus. This is the
no nucleus but have a unique, tough outer cell wall. archaeon most often isolated and most well known
This tough wall contains molecules and enzymes that by scientists. In sulfuric hydrothermal areas, it oxi-
may keep acid out of the organism, allowing it to live dizes sulfur into sulfuric acid, which helps dissolve
in environments of pH 3 or less. (For example, most the rocks into mud. The Sulfolobus community in
vinegar has a pH of less than 3.) Archaea also have Congress Pool (Norris) is providing interesting new
protective enzymes within their cells to keep them research directions for scientists: It is parasitized by
from becoming too acidic. viruses never before known on Earth.
Some scientists think present-day Archaea have not
changed much from their ancestors. This may be due
to the extreme environments in which they live, which
would allow little chance for successful changes to
occur. If this is so, modern Archaea may not be much
different from the original forms—and thus may pro-
vide an important link with Earth’s earliest life forms.
Once thought to be Bacteria, organisms in the
domain Archaea actually may be more closely related
to Eukarya—which includes plants and animals.
Many kinds of Archaea live in the hydrothermal
waters of Yellowstone. For example, Grand Prismatic
Spring at Midway Geyser Basin contains Archaea.
Archaea can be found in the Mud Volcano area,
They are most well known in the superheated acidic
among other places in Yellowstone National Park.
Thermophilic Archea found in Yellowstone National Park
Name pH and Temperature Description Location
Domain Archaea pH 0.9–9.8 Color: cream or yellow-colored • In many of Yellowstone’s
upper temp.: 92°C Metabolism: chemosynthesis, using hydrothermal features
(197.6°F) hydrogen, sulfur, carbon dioxide
Form: unicellular, tough cell
membrane
Sulfolobus pH 0–4, Color: cream or yellow-colored • Norris Geyser Basin
is the genus ~50–80°C (104–131°F) Metabolism: chemosynthesis • Lemonade Creek
most often
isolated
Life in Extreme Heat 143
T H E RMOP H I LE S
Microscopic Eukarya live unseen in the extreme environments of Yellowstone. Norris Geyser Basin is one of the
best places in Yellowstone to see thermophilic algae.
Thermophilic Eukarya Zygogonium are especially easy to see in Porcelain
Plants, animals, and mushrooms are the Eukarya Basin, where their dark colors contrast with the white
most of us know. However, millions of unseen, mi- surface.
croscopic members of this kingdom exist throughout From the boardwalk crossing Porcelain Basin, you
our world, including in the extreme environments of can also see larger Eukarya, such as ephydrid flies.
Yellowstone. They live among the thermophilic mats and stream-
Norris Geyser Basin is one of the best ers, and eat algae, among other things. The species
places to see thermophilic algae. Bright green that lives in the waters of Geyser Hill, in the Upper
Cyanidioschyzon grows on top of orange-red iron Geyser Basin, lays its eggs in pink-orange mounds,
deposits around Whirligig and Echinus geysers sometimes on the firm surfaces of the mats. Part of
and their runoff channels. Waving streamers of the thermophilic food chain, ephydrid flies become
prey for spiders, beetles, and birds.
Some microscopic Eukarya consume other ther-
mophiles. A predatory protozoan called Vorticella
thrives in the warm, acidic waters of Obsidian Creek,
which flows north toward Mammoth Hot Springs,
where it consumes thermophilic bacteria.
Thermophilic eukarya include one form that is
dangerous to humans: Naegleria, a type of amoeba
that can cause disease and death in humans if inhaled
through the nose.
Although they aren’t visible like mushrooms,
several thermophilic fungi thrive in Yellowstone.
UNIVERSITY
THERMAL BIOLOGY INSTITUTE, MONTANA STATE
Counterclockwise from top: Ephydrid flies lay eggs in pink-orange mounds, sometimes on the firm surfaces of
the mats; waving streamers of Zygogonium are easy to see in Porcelain Basin; the fungi Curvularia protuberata
lives in the roots of hot springs panic grass.
144 Yellowstone Resources and Issues Handbook, 2022
T H E RMOP H ILE S
Curvularia protuberata lives in the roots of hot thermophilic species thriving in Yellowstone’s ex-
springs panic grass. This association helps both or- treme environments, the Eukarya are the group that
ganisms survive higher temperatures than each could bridges the world of thermophilic microbes with the
alone. In addition, researchers have recently discov- larger life forms—such as geese, elk, and bison—that
ered a virus inside the fungus that is also essential to thrive in ecological communities beyond the hot
the grass’s ability to grow on hot ground. springs.
Of all the thousands, if not millions, of
Thermophilic Eukarya found in Yellowstone National Park
pH and
Name Description Location
Temperature
Red algae pH 0–4 Color: bright green • Norris Geyser Basin
Cyanidio 40–55°C Metabolism: photosynthetic • Lemonade Creek
schyzon (104–131°F) Form: coating on top of • Nymph Creek
formations; mats
Green algae pH 0–4 Color: appears black or dark
Zygogonium
T H E RMOP H I LE S
A virus was discovered in Congress Pool, shown here, at Norris Geyser Basin. It was infecting the archaean
Sulfolobus.
THERMAL BIOLOGY INSTITUTE, MONTANA STATE UNIVERSITY
Thermophilic Viruses
Like Bacteria, the word “virus” often conjures up
images of sickness and death. However, relatively
few of the many types of viruses cause problems
for humans. None of the thermophilic viruses in
Yellowstone should cause problems for human
health—our bodies are too cold, for one thing.
Unlike microorganisms in the three domains,
viruses are not considered to be alive, yet they are still
called “life forms.” They have no cell structure, only
a protein “envelope” that encloses genetic material.
They cannot reproduce on their own. Instead, a virus
inserts itself into a host cell and uses that cell’s nutri-
ents and metabolism to produce more viruses.
Scientists suspect many viruses exist in
Yellowstone’s hydrothermal features because they
would be a logical part of the thermophilic ecosys-
tem. One kind was discovered in Congress Pool, at This virus parasitizes Sulfolobus.
Norris Geyser Basin. It was infecting the archaeon
Sulfolobus. Another kind of virus has been identified
in pools near Midway Geyser Basin.
Thermophilic Viruses found in Yellowstone National Park
Name pH and Temperature Description Location
Viruses (not in a pH 0.9–5.8; optimum • Protein coats a core of genetic • In many of Yellowstone’s
domain) 2–3 material hydrothermal features
55–80°C (131–176°F) • Cannot reproduce by itself
optimum 70–75°C • Reproduces by using the host
cell’s metabolism
• Not considered living
• Predators of other microbes
Unnamed Acidic • Shape very similar to viruses • Unnamed pool near Midway
Boiling that infect Bacteria and Geyser Basin
animals, which could mean this
group of viruses existed early
in the development of life on
Earth
Unnamed Acidic • Parasitizes the archaean, • Norris, Congress Pool
Boiling Sulfolobus
146 Yellowstone Resources and Issues Handbook, 2022
T H E RMOP H ILE S
Channels formed with water runoff from geysers create bacterial columns such as this one, located where the
runoff channels from Pinwheel and Whirligig geysers meet.
199°F (93°C)
Thermophilic Communities communities as light, Archaea
Thermophilic communities are as diverse as the com- temperature, and
munities that humans live in. Community formations, chemical concentrations
colors, and locations vary depending on the types change—both short term
of microbes, the pH, and the temperature of their (within one day) and
environments. Here, we discuss the microbe commu- long-term (seasonally). 163°F (73°C)
Cyanobacteria
nities most easily seen in Yellowstone. As day brightens to noon,
Millions of individual microbes can connect into Cyanobacteria sensitive to
long strands called filaments. Some Bacteria and light may move away from
algae form thin and delicate structures in fast moving the surface; microbes 144°F (62°C)
water such as the runoff channels of hot springs and less sensitive to light may Fungi
geysers. Other microbes form thick, sturdy struc- move to the top layers of 140°F (60°C)
tures in slower water or where chemical precipitates the mat. When light levels Algae
quickly coat their filaments. cause shifts in organ-
A bacterium called Thermocrinis forms structures isms, the community
and is descended from ancient Bacteria that metabo- is responding to a light
lized hydrogen and oxygen. Its filaments entwine, gradient. 133°F (56°C)
Protozoa
forming mats. Flowing water carries other microbes, Temperature and
organic matter, and minerals that become caught in chemical gradients most
the streamers and add to the mat. often affect thermophilic 122°F (50°C)
Photosynthetic activity of Cyanobacteria such as communities in runoff Mosses,
Lyptolyngbya form columns or pedestals. Oxygen channels of geysers and crustaceans,
and insects
bubbles rise in the mat, forcing the microbes upward. in shallow outflows from
The higher formations capture more organic matter hot springs. The runoff
and sediment than the lower mats, which help build channels from Pinwheel
the columns. Called stromatolites or microbialites, and Whirligig geysers
these structures are similar to ancient microbial com- meet. The outer edges
munities preserved in formations around the world. of both are too hot for
Mats can be as thin as tissue paper or as thick as visible thermophile com-
80°F (27°C)
lasagna. Multiple layers of microorganisms make up munities to develop. But
Trout
inch-thick mats. Dozens of types of microbes from all as Pinwheel’s water cools
three domains can exist in these layers. Each layer is in the shallower chan- Thermophilic community
a community, and each layer interacts with the other nel edge, Cyanidium (an inhabitants are
layers, forming a complex, larger community full of alga) can grow, forming controlled, in part, by
water temperature and
millions of microorganisms and their life processes. a bright green commu-
pH. The chart provides
nity. Whirligig’s runoff general guidelines for
Changes in Communities is hotter, which pre- maximum for each type.
Visible and invisible changes occur in thermophile vents Cyanidium from
Life in Extreme Heat 147
T H E RMOP H I LE S
COURTESY CAROLYN DUCKWORTH
growing, but another type of thermophile thrives by
oxidizing the abundant iron in the water, thereby
forming the orange/red colored community.
At the Chocolate Pots, which you can see from
pullouts along the Gibbon River just north of
Gibbon Meadows, iron-rich water flows from the
vents. Cyanobacteria—such as Synechococcus, and
Oscillatoria—thrive in this feature. The bacterial
filaments form mats, in which orange-red iron oxide
(rust) is captured. The iron may also be caught on
the Bacteria as the microbes move about within the
mat. An olive green color indicates where the or-
ange iron and green bacteria are enmeshed. Darker Bison and elk find food and warmth on the less
streaks indicate the presence of manganese. Scientists extreme edges of thermophilic environments in
think that mixing of iron-rich waters with shallow winter.
Thermophiles by Place and Color in Yellowstone National Park
Location Characteristics Thermophiles by Temperature Thermophiles by Color
Upper, Middle, and Lower Geyser Basins and West Thumb Geyser Basin
• pH 7–11 • >75°C (167°F), Bacteria and • Pink, yellow, orange, gray
(alkaline) Archaea filaments—Thermocrinis
• underlain by • >75°C (167°F), Thermocrinis and bacteria
rhyolitic rock other bacteria form streamers of • Orange mats—Cyanobacteria,
• water rich pink, yellow, orange, or gray especially on sunny summer
in silica, • 75°C (167°F), Sulfolobus, an • Pink–pinkish-orange mats and
(acidic) archaean, and viruses that streamers—Thermus aquaticus
• underlain by parasitize Sulfolobus and other Thermus sp.
rhyolite rock • >60°C (140°F), filamentous bacteria • Green streamers and mats—
in yellowish streamers and mats Cyanidium
•T H E RMOP H ILE S
THERMAL BIOLOGY INSTITUTE, MONTANA STATE UNIVERSITY
shift in heat beneath the Earth, these communities
change through both common and strange processes.
Biologists continue to discover more about the indi-
viduals involved in thermophilic communities, and
ecologists follow the threads of these intricate webs.
Thermophiles in Time and Space
To Mars—and Beyond?
The hydrothermal features of Yellowstone and their
associated thermophilic communities are studied
by scientists searching for evidence of life on other
planets. The connection is extreme environments. If
life began in the extreme conditions thought to have
been widespread on ancient Earth, it may well have
developed on other planets with similar conditions—
and these conditions might still exist today.
The chemosynthetic microbes that thrive in some
of Yellowstone’s hot springs do so by metabolizing
inorganic chemicals, a source of energy that does not
require sunlight. Such chemical energy sources pro-
vide the most likely habitable niches for life on Mars
Top: Structures formed by the bacteria Thermocrinis. or on the moons of Jupiter—Ganymede, Europa, and
Bottom: Millions of individual microbes can connect Callisto—where uninhabitable surface conditions
into long strands called filaments, shown here with the preclude photosynthesis. Chemical energy sources,
help of a microscope.
precipitation-derived waters creates the unique con-
What’s the Connection?
ditions that give rise to the large iron and manganese
oxide mounds at Chocolate Pots. These formations • Yellowstone’s hydrothermal features contain modern
are not commonly encountered in the park. examples of Earth’s earliest life forms, both chemo-
and photosynthetic, and thus provide a window into
Communities formed by thermophilic microbes Earth’s ancient past.
sustain communities of larger organisms within
• Yellowstone’s hydrothermal communities reveal
Yellowstone’s hydrothermal areas. These communi- the extremes life can endure, providing clues to
ties in turn affect even larger communities of the environments that might harbor life on other worlds.
park’s mammals. For example, bison and elk find • Yellowstone’s environments show how mineralization
food and warmth on the less extreme edges of ther- preserves biosignatures of thermophilic communities,
which could help scientists recognize similar
mophilic environments in winter. In turn, coyotes, signatures elsewhere.
wolves, and bears seek prey in these areas—especially
• Based on life on Earth, the search for life on other
in late winter and early spring when bison and elk are planets seems more likely to encounter evidence of
weaker than at any other time of year. microorganisms than of more complex life.
Whether it’s the strike of a grizzly’s paw or a
Earth formed
Era of chemical Age of microorganisms Age of mammals
evolution
Earth’s crust stabilizing
Oxygen atmosphere forming Age of dinosaurs
4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
Billions of years ago
Life in Extreme Heat 149T H E RMOP H I LE S
NASA/JPL
along with extensive groundwater systems (such as
on Mars) or oceans beneath icy crusts (such as on
Jupiter’s moons) could provide habitats for life.
Similar Signatures
Thermophile communities leave behind evidence of
their shapes as biological “signatures.” For example,
at Mammoth Hot Springs, rapidly depositing min-
erals entomb thermophile communities. Scientists
compare these modern signatures to those of an-
cient deposits elsewhere, such as sinter deposits in
Australia that are 350 billion years old. These com-
parisons help scientists better understand the envi-
ronment and evolution on early Earth, and give them
an idea of what to look for on other planets.
Yellowstone National Park will continue to be an
These layers of rock on Mars have minerals and
important site for studies at the physical and chemical features developed by interactions between liquid
limits of survival. These studies will give scientists a water and rocks over time. This evidence does not
better understanding of the conditions that give rise prove life developed on Mars, but it brings the
to and support life, and of how to recognize signa- possibility one step closer to reality. Photo and caption
adapted from www.nasa.gov, image by NASA/JPL.
tures of life in ancient rocks and on distant planets.
Reviewers
Dr. Eric Boyd, Montana State University Department of
Microbiology and Immunology
Dr. Erin White, Park Hydrologist
Annie Carlson, Research Permit Coordinator
150 Yellowstone Resources and Issues Handbook, 2022You can also read
