Life in Extreme Heat

A bubbling blue pool of water with orange edges surrounded by other colorful pools and a forest edge
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 Firehole Spring.

NPS/Jim Peaco


The hydrothermal features of Yellowstone are magnificent evidence of Earth’s volcanic activity. Amazingly, they are also habitats in which microscopic organisms called thermophiles—“thermo” for heat, “phile” for lover—survive and thrive.

Grand Prismatic Spring at Midway Geyser Basin is an outstanding example of this dual characteristic. Visitors marvel at its size and brilliant colors. Along the boardwalk we cross a vast habitat for thermophiles. Nourished by energy and chemical building blocks available in the hot springs, microbes construct vividly colored communities. Living with these microscopic life forms are larger examples of life in extreme environments, such as mites, flies, spiders, and plants.

People for thousands of years likely have wondered about these extreme habitats. The color of Yellowstone’s superheated environments certainly caused geologist Walter Harvey Weed to pause and think, and even question scientists who preceded him. In 1889, he wrote:

There is good reason to believe that the existence of algae of other colors, particularly the pink, yellow and red forms so common in the Yellowstone waters, have been overlooked or mistaken for deposits of purely mineral matter.

However, he could not have imagined what a fantastic world exists in these waters of brimstone. Species, unseen to the human eye, thrive in waters as acidic as the liquid in your car battery and hot enough to blister your skin. Some create layers that look like molten wax on the surface of steaming alkaline pools. Still others, apparent to us through the odors they create, exist only in murky, sulfuric caldrons that stink worse than rotten eggs.

Today, many scientists study Yellowstone’s thermophiles. Some of these microbes are similar to the first life forms capable of photosynthesis—using sunlight to convert water and carbon dioxide to oxygen, sugars, and other by-products. These life forms, called cyanobacteria, began to create an atmosphere that would eventually support human life. Cyanobacteria are found in some of the colorful mats and streamers of Yellowstone’s hot springs.

Tree of Life
Yellowstone’s hot springs contain species from the circled groups on this Tree of Life. Jack Farmer conceived of this version of the tree of life, which first appeared in GSA Today, July 2000 (used with permission).

Mary Ann Franke

Thermophiles in the Tree of Life

In the last few decades, microbial research has led to a revised tree of life, far different from the one taught before. The new tree combines animal, plant, and fungi in one branch. The other two branches consist solely of microorganisms, including an entire branch of microorganisms not known until the 1970s—Archaea.

Dr. Carl Woese first proposed this “tree” in the 1970s. He also proposed the new branch, Archaea, which includes many microorganisms formerly considered bacteria. The red line links the earliest organisms that evolved from a common ancestor. These are all hyperthermophiles, which thrive in water above 176°F (80°C), indicating life may have arisen in hot environments on the young earth.

Relevance to Yellowstone

Among the earliest organisms to evolve on Earth were microorganisms whose descendants are found today in extreme high-temperature, and in some cases acidic, environments, such as those in Yellowstone. Their history exhibits principles of ecology and ways in which geologic processes might have influenced biological evolution.


About Microbes

Other life forms—the Archaea —predated cyanobacteria and other photosynthesizers. Archaea can live in the hottest, most acidic conditions in Yellowstone; their relatives are considered among the very earliest life forms on Earth.

Yellowstone’s thermophiles and their environments provide a living laboratory for scientists, who continue to explore these extraordinary organisms. They know many mysteries of Yellowstone’s extreme environments remain to be revealed.

Regardless of scientific advances, visitors and explorers in Yellowstone can still relate to something else Weed said about Yellowstone, more than a century ago:

The vegetation of the acid waters is seldom a conspicuous feature of the springs. But in the alkaline waters that characterize the geyser basins, and in the carbonated, calcareous waters of the Mammoth Hot Springs, the case is otherwise, and the red and yellow tinges of the algae combine with the weird whiteness of the sinter and the varied blue and green of the hot water to form a scene that is, without doubt, one of the most beautiful as well as one of the strangest sights in the world.
Archaea are found in place like the mudpots of Mud Volcano.

Thermophilic Archaea

Archaea are the most extreme of all extremophiles.

Traverine terraces of Mammoth Hot Springs host thermophilic bacteria.

Thermophilic Bacteria

Almost all hot springs and geysers host thermophilic bacteria.

Green colors line a thermal runoff pool.

Thermophilic Eukarya

Microscopic plants and animals live in the extreme environments of Yellowstone's hydrothermal features.

Blue waters of Congress Pool are host to thermophilic viruses

Thermophilic Viruses

Viruses, a logical part of thermophilic ecosystems, have been found in some pools in Yellowstone.

Orange-colered bacterial column growing in geyser runoff water.

Thermophilic Communities

Thermophilic communities are very diverse, depending on the microbes living there, the pH, and the water temperature.

The rainbow colors of Grand Prismatic Spring range from blue to orange.

Hydrothermal Systems

Yellowstone's hydrothermal systems are the visible expression of the immense Yellowstone volcano.

Eruption plume of Great Fountain Geyser.

Hydrothermal Features

Yellowstone preserves earth's most extraordinary collection of hot springs, geysers, mudpots, fumaroles, and travertine terraces.

View of the

Thermophiles in Time & Space

Yellowstone's hydrothermal features and thermophilic communities are studied by scientists searching for evidence of life on other planets.

Green and brown bacterial mats growing in runoff water.


Bioprospecting is the discovery of useful scientific information from genetic or biochemical resources.



American Society for Microbiology:

Allen, E. T., Arthur L. Day, and H.E. Merwin. 1935. Hot springs of the Yellowstone national park. [Washington]: Carnegie institution of Washington.

Brock, T.D. 1994. Life at High Temperatures. Yellowstone Association/Mammoth, WY.

Brock, Thomas D. 1995. The road to Yellowstone and beyond. Annual Review of Microbiology. 49

Dyer, B.D. 2003. A field guide to bacteria. Ithaca, NY: Cornell University Press.

Franke, M.A, et. al. 2013. Genetic Diversity in Yellowstone Lake: The Hot and Cold Spots. Yellowstone Science 21 (1): 6-22.

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Klatt, C. G., et. al. 2011. Community ecology of hot spring cyanobacterial mats: predominant populations and their functional potential. ISME Journal. 5(8): 1262–1278.

Marquez, Luis et al. 2007. A virus in a fungus in a plant: 3-way symbiosis required for thermal tolerance. Science 315 (5811): 513–515.

Qin, J., C.R. Lehr, C. Yuan, X. C. Le, T. R. McDermott, and B. P. Rosen. Biotransformation of arsenic by a Yellowstone thermoacidophilic eukaryotic alga. Proceedings of the National Academy of Sciences of the United States of America. 106 (13): 5213.

Reysenbach, A.L., and Shock, E. L. 2002 . Merging Genomes with Geochemistry in Hydrothermal Ecosystems. Science. 296: 1077-1082.

Sheehan, K.B. et al. 2005. Seen and unseen: discovering the microbes of Yellowstone. Guilford, Conn: Falcon.

Snyder, J.C. et. al. 2013. Functional interplay between a virus and the ESCRT machinery in Archaea. Proceedings of the National Academy of Sciences. 110 (26) 10783-10787.

Spear, J. R. et. al. 2005. Hydrogen and bioenergetics in the Yellowstone geothermal ecosystem. Proceedings of the National Academy of Sciences. 102 (7) 2555-2560.

Steunou A.S., et. al. 2008. Regulation of nif gene expression and the energetics of N2 fixation over the diel cycle in a hot spring microbial mat. ISME Journal. (4):364-78.

Takacs-Vesbach, C., et al. 2013. Metagenome sequence analysis of filamentous microbial communities obtained from geochemically distinct geothermal channels reveals specialization of three aquificales lineages. Frontiers Research Foundation.

Thermal Biology Institute of Montana State University:

Ward, D.M., Castenholz, D.W., and Miller, S.R. 2012. Cyanobacteria in Geothermal Habitats. In Brian A. Whitton, ed. Ecology of cyanobacteria II: their diversity in space and time. Dordrecht: Springer

Last updated: August 21, 2017

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