Mammoth Hot Springs is a large complex of colorful hot springs containing microbes, called extremophiles, located on a hill of in Yellowstone National Park^[1]. Yellowstone's Mammoth Hot Springs was created over thousands of years as hot water cooled and deposited calcium carbonate (over two tons flow into Mammoth each day in solution). Although these springs lie outside the caldera boundary, the heat energy that created and sustains them is attributed to the same magmatic system that fuels other Yellowstone geothermal areas. The organisms that create the distinctive color collage of Mammoth Hot Springs are known as extremophiles.^[2]

Extremophiles are a group of microscopic organisms called microbes. Microbes are microorganisms that are usually observed with the help of a microscope. Microbes were first discovered by Anton van Leeuwenhoek in 1675,^[3] who invented and used his own microscope to discover and identify the existence of microbes. Before van Leeuwenhoek's discovery, theories about the existence of microbes had been offered by men of science and medicine, such as Roman scientist, Marcus Terentius Varro in the 1st century BC. However, until van Leeuwenhoek's discovery, there was no observable proof about the existence of microbes.

Microorganisms (microbes) include bacteria, fungi, algae, and protozoa; microscopic plants (green algae); and animals such as rotifers and planarians. Extremophiles are microbes that survive and thrive under extreme physical and biochemical conditions. Yellowstone is one of the most renowned places on Earth to study extremophiles due to their diversity and ease of access. Yellowstone contains about half (more than 10,000) of the worlds hydrothermal features such as geysers (e.g.: Old Faithful); fumaroles;^[4] mudpots,^[5] and hot springs.

The NASA Astrobiology Institute (NAI)^[6] has undertaken various studies of Yellowstone's extremophiles because they represent the first life forms to inhabit Earth. Extremophiles are believed to be the only life form existing on Earth for the first half of life's presence on this planet. Also, due to the biochemical abilities of extremophiles to survive under extreme environmental conditions - it is theorized that extremophiles may also live on other planets and moons.

Each color present in the terraces of Mammoth Hot Springs represents a different family, or collection of microbes with specific biochemical and temperature requirements. As the temperature of the water and the air changes - so will the colors of the hot springs.