Life in Extreme Heat

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10 minutes, 54 seconds

Learn about these amazing organisms that live in some of the hottest environment on earth—including in Yellowstone's hydrothermal features.


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. The boardwalk crosses 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.

For thousands of years, people have likely wondered about these extreme habitats. The color of Yellowstone’s superheated environments certainly caused geologist Walter Harvey Weed to pause, 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—the process of 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.

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

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—the 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 ancestor of the Bacteria, Archaea, and Eukarya is inferred to be where the blue, red, and green lines connect. Organisms that branch closest to this ancestor are 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. Researchers know that 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 that geologist Walter Harvey Weed wrote 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.

Science Articles on Thermophiles

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    Source: Data Store Collection 7681. To search for additional information, visit the Data Store.

    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.

    A deep, blue and green hot spring.
    Hydrothermal Features

    Learn about hot springs, geysers, mudpots, and fumaroles.

    View of the "Burns Cliff" on Mars showing rock layers with evidence of water reactions.
    Thermophiles in Time and 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.

    A bull elk bugling

    Discover the natural wonder of Yellowstone, from the geology beneath the plant communities to the animals migrating through the ecosystem.

    Last updated: November 27, 2023

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