Discovering Life in Yellowstone Where Nobody Thought it Could Exist

By Marybeth Shea, University of Maryland College Park

This article, and others in the series "Parks in Science History", was written by a graduate student at the University of Maryland. The articles highlight the roles that national parks have played in the history of science and, therefore, the world's intellectual heritage. More articles and videos will be produced in the future.
A close-up image of yellow, brown and white bacteria in a thermal pool
Thermophilic bacteria in Yellowstone National Park.

NPS Photo / Neal Herbert

Visitors to Yellowstone National Park in Wyoming encounter many visual treats, from the spectacular Lower Falls in the Grand Canyon of the Yellowstone River and the iconic Old Faithful Geyser, to the bison and wolves living in the nation’s first national park. Even small scale views in Yellowstone are compelling, especially the colors in hot pots and deep pools. But far from being merely aesthetically pleasing, these colors are significant because they sparked an important scientific inquiry with long-lasting implications for science, technology, and society.

Scene: A Ranger Talk in the 1960s

Thomas Brock, a vacationing bacteriologist and microbiology professor, visited Yellowstone to break up a long car trip. Brock recalled that 1964 day:

“I got out of the car and, by chance, a ranger was giving a talk near a thermal pool. I saw all this color, and he said it was blue-green algae. I got interested right away.”

Brock agreed with the ranger’s identification of blue-green algae but he was deeply curious that this microorganism was living -- likely thriving -- at such a high temperature. Many hot pools in Yellowstone approach or even exceed the boiling point of water.
A colorful thermal pool surrounded by white snow
Morning Glory Pool during winter.

NPS Photo

In sustained fieldwork from 1965 to 1971, Brock took samples from the many hot pots, geyser pools, fumaroles (steam vents), and thermal basins of the Firehole River watershed. He found microbes in all of these extremely hot environments, including a previously unknown species that Brock named Thermus aquaticus, with his colleague Hudson Freeze.

Later, Brock expanded his sampling locations to include thermal pools in California, other global sites, and even hot water taps. T. aquaticus lived in those places, too. Brock discovered that microbes did, indeed, live in extremely hot environments. Previous scientific work suggested that such extreme environments could not support life. Brock was about to both counter this established knowledge and open an entirely new line of scientific study. Brock’s groundbreaking 1967 paper published in the journal Science claimed that, based on his work begun in Yellowstone National Park,

“It is thus impossible to conclude that there is any ‘upper temperature of life.’”

As is the practice in microbiology, Brock submitted his sample of Thermus aquaticus, from Yellowstone’s Mushroom Pool, to the American Type Culture Collection of the American Microbiology Society, where this freeze-dried sample remains today. This collection is a depository of species tissues that are distributed for research and technical uses.
A thermal pool with drown edges and a dark center
Mushroom Pool

NPS Photo

Picture of Thomas Brock
Thomas Brock

Long-Lasting Significance

Brock’s discovery changed scientific thinking about a fundamental condition of life: the range of temperatures in which organisms can exist. Microbiologists worldwide started to look for other microbes in extreme conditions. They found diverse species of microbes living in conditions with extreme heat, cold, aridity, pH, and other conditions. Today, scientists refer to these organisms collectively as extremophiles.

This powerful new knowledge about the range of microbial environments is not the only finding traced to that 1964 day in Yellowstone. By the late 1980s, biochemist Kary Mullis sought a better way to examine DNA molecules. For his test-tube reactions, he needed an enzyme to make millions of copies of a single DNA molecule. And that enzyme had to work at high temperatures. Mullis browsed the American Type Culture Collection, lingering on the sample that Brock collected in the very hot Mushroom Pool.

Colleague David Gelfand purchased an amount of this Thermus aquaticus culture and Mullis grew large batches of the culture to find the enzyme Taq polymerase (Taq). This enzyme fit perfectly Mullis’ technology goal because Taq’s heat resistant property enabled Mullis to rapidly and inexpensively copy genes and determine their unique chemical sequences. This Taq-enabled test-tube process is called Polymerase Chain Reaction (PCR); without PCR, modern biotechnology likely could not have advanced in the time frame we now all benefit from. Mullis won the 1993 Nobel Prize in chemistry for his invention of PCR.
PCR enables the sequencing of genes by working with DNA structure. The tool of PCR, in turn, enabled scientists to identify species and establish evolutionary relationships among them. Interestingly, microbial ecology, a field that Brock helped build, relies on PCR, too. PCR opened up many vistas for both science and society. Here are a few:
  • PCR makes possible both medical diagnosis and treatments where genetic information is key to improving health.
  • People who now enjoy a genealogy or health DNA profile rely on PCR.
  • Police and the courts also use PCR to identify criminals, determine paternity, and other complex matters.
  • More recently, environmental scientists use PCR and other DNA techniques to track pollution, monitor ecosystem health, and conserve species. This work is underway on many federal and state public lands.

What does Brock think about his work in Yellowstone long ago? In a July 13, 2018 phone interview, Brock commented on a few aspects of his work.

He notes that his initial research questions about heat and microbes are best understood as basic research compared to applied research. Indeed, Brock’s fundamental discovery in Yellowstone extended the field of medical bacteriology to ignite the field of microbial ecology. Brock is grateful for both university and later government support to make his inquiries. He hopes that basic research support will be understood as important, in this era of applied research preferences.

Fieldwork, supported by lab analysis, was key to these findings. Brock enjoyed both support and cooperation with Yellowstone National Park managers and rangers. Many colleagues and graduate students joined Brock and his core team to study heat-resistant microbes but also other aspects of biogeological research questions.

Interdisciplinary research is an approach essential for both ecology and the environmental sciences that support practical understanding for the complex ecosystems of many National Park system locations.

Brock concluded by commenting on the extraordinary natural beauty of Yellowstone, saying, “I am very lucky to have been able to spend 10 years doing research in Yellowstone, one of the most exciting places on the planet.”


Brock, T.D. (1964). Life at High Temperatures, published in booklet form by the Yellowstone Association for Natural Science, History & Education, Inc.

Yellowstone National Park, Wyoming 82190. PDF available at

Brock TD & Freeze H (1969). "Thermus aquaticus, a Nonsporulating Extreme Thermophile". J. Bacteriol. 98 (1): 289–97. PMC 249935  . PMID 5781580.

Brock, Thomas D. (August 1, 1997). "The Value of Basic Research: Discovery of Thermus aquaticus and Other Extreme Thermophiles". Genetics. 146 (4): 1207–10. PMC 1208068  . PMID 9258667.

Part of a series of articles titled Parks in Science History.

Yellowstone National Park

Last updated: November 8, 2018