Grand Prismatic: The Color Is Alive

The rings of color you see from the overlook trail are not mineral deposits. They are not geological pigmentation. They are living organisms, billions of them, arranged in concentric bands according to how much heat they can tolerate.

At the center of Grand Prismatic Spring, water rises from underground at roughly one hundred sixty degrees Fahrenheit. Nothing photosynthetic can survive that. The deep blue is the color of the water itself, sterile and superheated. Moving outward, as the water cools, different species of thermophilic bacteria colonize the temperature band they are adapted to. Green, then yellow, then orange, then brown at the cool edges where the organisms are most dense. The spring is approximately three hundred seventy feet across, large enough that early visitors measured it by riding a horse to its edge and estimating. It discharges an estimated five hundred sixty gallons per minute.

Geologist Ferdinand Hayden described it in eighteen seventy-one during the first major government survey of Yellowstone. The colors he documented were the same colors visible today, because the bacterial communities have been evolving in these springs for far longer than the park has existed.

In the nineteen sixties, a microbiologist named Thomas Brock began studying life in Yellowstone's hot springs. He isolated a heat-tolerant bacterium from a spring near here, Thermus aquaticus. The enzyme extracted from that organism later became the basis for the polymerase chain reaction, the DNA amplification technique used in forensic science, medical diagnostics, and the testing that identified COVID-nineteen. The most photographed feature in Yellowstone produced a molecule that changed biology. The bacteria were here first.