Life in the Cauldron

Meet the hearty tenants of Yellowstone’s deadly hot springs. /

How many are your works, Lord!
In wisdom you made them all;
the earth is full of your creatures.

All creatures look to you
to give them their food at the proper time.

–Psalm 104:24, 27

Few experiences bring me more joy than my yearly fly-fishing trips to the Northwest Mountain States. In the bitter Illinois winter, I find myself swiping through images on my phone of the region’s many fishable rivers: the rough-and-tumble Box Canyon stretch of Henry’s Fork, the fast-paced runs and slicks of the Madison, the breathtaking mountain views of the Gallatin. But one of my favorite memories is wading in the Firehole River in the western section of Yellowstone National Park, tufts of snow drifting down to disappear on the water’s surface, wisps of steam rising from nearby hot springs. Bison lie in the whitening grass on the opposite bank, uninterested in my casting. The only outlier in this moment of serene beauty is a slight smell of rotten eggs.

This odor, emanating from the hot springs and other hydrothermal features that give the Firehole River its name, provide the tiniest whiff of a startling truth about Yellowstone: the park rests upon a massive supervolcano. “I’ve long believed,” says geophysicist Robert Smith, “that when visitors come into the park they could be greeted with a sign that says, ‘Welcome to Yellowstone—you’re now entering a volcano.’”

The rotten egg smell is the result of bacteria (such as Desulfovibrio vulgaris) that feed off sulfides and create hydrogen sulfide as a byproduct. These anaerobic bacteria thrive without oxygen, living in water deep beneath the earth’s surface. This water is heated by the great cove of magma located beneath the Yellowstone Caldera (or crater) and rises rapidly to the spew into the air as spray from a geyser or steam from a hot spring.

It’s strange to think of life existing in such an inhospitable place, but that is one of Yellowstone’s most remarkable features at the macro and the micro levels. In fact, it’s the area’s volatility, not its tranquility, that attracted crowds of people in the first place. Yellowstone was designated the first national park in the world because of its hydrothermal features, most notably the Old Faithful geyser, and tourists have been flooding into the park ever since. Yellowstone’s status as a national park transformed it into a sanctuary of sorts, preserving it as one of the world’s largest nearly-intact temperate-zone ecosystems. Yellowstone’s elk, moose, bison, grizzlies, and—yes—trout are indebted to the park’s hydrothermal wonders.

Several plants, too, thrive in the park, not in spite of the geothermal features, but because of them. Yellowstone sulfur buckwheat, Yellowstone sand verbena, and Ross’s bentgrass are the park’s three endemic plants which need the presence of ground heat to survive Yellowstone’s harsh winters and cool summers. Ross’s bentgrass, in particular, thrives in geothermally warmed, moist sites, such as the walls of thermal springs, along steaming cracks, or in thermally influenced depressions.

Still, neither flora nor fauna can survive too close to the simmering hot springs. As with the aposematic coloration of tree frogs and cuttlefish, hot springs’ attractive radial patterns of blue, green, orange, and white belie their hazardous nature. The water within can reach temperatures of 205 degrees Fahrenheit, and the most acidic pools in the park have a pH of 2 (the same as stomach acid). Twenty-two people have died in the thermal waters of Yellowstone since 1890, the most recent in June 2016. Less than a day after this man strayed from the boardwalk, slipped, and fell into a hot spring, rescuers suspended their search for his body because “it was determined that there were no remains to recover.”

Yet life thrives even in what astronomer Jill Tarter calls “the boiling battery acid of Yellowstone hot springs.” The pink, orange, and white rings encircling many of the park’s hot springs and geysers, which many misidentify as mineral deposits, are composed of millions of microorganisms.

Anything else would die in these environments. But most of these thermophiles—“thermo” for heat and “phile” for lover—photosynthesize, converting carbon dioxide, sunlight, and water into sugar, oxygen, and water. A few of these bacteria chemosynthesize, producing the rotten-egg smell that accompanies many of Yellowstone’s hydrothermal features. Bacteria line themselves end to end, forming filaments that bind together into mats, as thin as tissue paper or as thick as lasagna.

Scientists knew about the existence of heat-loving bacteria early in the history of bacteriology. “It is curious,” wrote M. P. Miquel, the first man to discover thermophiles in 1881, “to see a living organism growing in a liquid medium where the hand is harshly burnt in a few seconds.” Early bacteriologists believed the upper limit for sustained bacterial life was 167 degrees Fahrenheit. Anything higher was out of the question. In the following years, even these cases were forgotten because the only people studying thermophiles were food bacteriologists, concerned with culturing bacteria that could spoil canned food. These scientists established 131 degrees as the upper limit for bacterial growth, and the search for thermophile bacteria in natural environments was dropped for over half a century. Unaware of the earlier studies of Miquel and others, biophysicist Ellis Kempner concluded as late as 1963 that no life could exist above the temperature of 163 degrees.

Then in 1966, microbiologist Thomas Brock discovered bacteria in Yellowstone’s Octopus Spring flourishing at 190 degrees. Among these hyperthermophiles living in the park’s hottest waters, Brock isolated a yellowish bacterium that he named Thermus aquaticus. Back in the lab, he was able to grow cultures of T. aquaticus at 174 degrees. His partner, Hudson Freeze, showed that enzymes from this bacterium could tolerate even higher temperatures, surviving water boiling at 212 degrees. This heat-resistant, DNA-copying enzyme led to great progress in microbiology, medicine, and agriculture, and helped establish the field of biotechnology.

An environment once considered uninhabitable has now proven to house a vast array of tiny tenants. Like Elijah in the Kerith Ravine or the Israelites in the Desert of Sin, Yellowstone’s thermophiles testify to God’s provision for his creatures, wherever they might live.

Kyle Rohane is managing editor of He wrote on synaptic pruning for issue 39 of The Behemoth.

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Also in this Issue

Issue 55 / August 18, 2016
  1. Editor's Note from August 18, 2016

    Issue 55: Seeking silences, Yellowstone's extreme life, and the ironies of wildfire. /

  2. Traveling into Silence

    A journey into two of the quietest places on earth. /

  3. Wildfire’s Dangerous Renewal

    Awe and lessons from Peshtigo, Yellowstone, and Fort McMurray. /

  4. Christ as a Gardner

    “I never noticed it until they died.” /

  5. Wonder on the Web

    Issue 55: Links to amazing stuff.

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