Billions of colorful microorganisms line this hot spring’s runoff channels, living as extremophiles in conditions once thought too extreme to host life. Those that live in hot springs are thermophiles, or heat-lovers. Within the rainbow of orange, brown, and red colors, some microorganisms live in thick mat communities with a vertical structure and stratified functions like miniature forests. Microbes on or near the top of the mat, like a forest canopy, use sunlight to perform photosynthesis, which fuels the mat community. Organisms deeper in the mat, like a forest understory, derive energy from chemicals produced by the surface microbes and perform vital functions such as decomposition and recycling nutrients back to the mat’s canopy. Together these organisms create an ecosystem within the space of a few inches. Yellowstone National Park is one of the most accessible places to study extreme environments and the organisms that inhabit them, and understanding lifeforms here provides clues for scientists searching for life elsewhere in the universe, where harsh planetary conditions suggest that any life would probably be some form of microscopic extremophile.

Photo: Dan Fisher

Photo: Bernard Fisher

Mammoth, Wyoming · USA