National Geographic : 2016 May
The colors of Grand Prismatic Spring come from thermophiles: microbes that thrive in scalding water. The green is chlorophyll they use to absorb sunlight. PHOTO: MICHAEL NICHOLS ‘Nothing ever conceived by human art could equal the peculiar vividness and delicacy of coloring of these remarkable prismatic springs,’ wrote Ferdinand Hayden, leader of an early expedition to Yellowstone. It was the landscape and especially the hot springs, more than the wildlife, that moved Congress to set the land aside as a park. Yet the colored springs conceal their own extreme wildlife—microbes that hint at what might live on other, harsher planets.