Justin and Eric led off with an introduction and history of the extremophile organisms of Yellowstone. They related how in the 1960s a bacteriologist named Thomas Brock began to look for bacteria in a warm creek downstream from a hot spring, and ended up finding organisms that thrived in the near-boiling water at the creek's source. The organism he found, Thermus aquaticus, was the first of the Archaea, ancient microorganisms now widely regarded as a separate kingdom of life. Subsequent discoveries have shown that Archaeans inhabit some of the most extreme environments on Earth. In addition to thermoacidophilic Archaeans, such as those found in Yellowstone, there are halophiles (thriving in very salty environments, such as the Dead Sea) and methanogens (which live in anaerobic conditions).

Jamie followed with his summary of how the acidity level (measured in pH) affects living organisms. In Yellowstone, the acidic hot pots have pH levels that range from 2 (as acid as lemon juice) to 4 (as acid as tomatoes). In many of these hot springs, the thermoacidophilic prokaryotes Sulfolobus or Acidianus, of the domain Archaea, are the only known inhabitants. These organisms oxidize elemental sulfur to sulfuric acid and use this energy to grow atrophically, and use carbon dioxide as their carbon source.

Tom spoke about the question: how hot can the surroundings be for living organisms? He said that, in general, plants and animals can survive temperatures higher than 50 degrees Celsius (122 F), but find it difficult or impossible to grow in environments that are constantly that high. Microorganisms are different - they can grow in temperatures well above 50 Celsius, in fact up to 115 Celsius, which is past the boiling point of water at sea level. Only the organisms in the domain Archaea are able to do this.

Tom pointed out that the organisms that live in the Yellowstone hot pots, Sulfolobus acidocaldarius and pyrobacterium brockii, thrive in high temperatures but aren't found if temperatures drop below around 160-175 F.

Jamie then showed some pictures taken during the field trip to the hot pots, and briefly explained the scientists' purpose and collection procedures.

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