Guide to the wildest life on Earth

Life fueled by hydrogen
Another recent extremophile study discovered microbes in the hot springs of Yellowstone National Park using hydrogen as their primary fuel source, refuting the popular conception that sulfur is the main source of energy for microbes living in thermal features.

The research was designed to find the main source of energy of microbes living in hot springs with temperatures over 158 degrees Fahrenheit (70 Celsius), a temperature too high for photosynthesis.

"It was a surprise to find hydrogen was the main energy source for microbes in hot springs," said University of Colorado researcher Norman Pace, who led the team.

Pace's colleague John Spear, lead author of the study published in January’s online edition of the Proceedings of the National Academy of Sciences, speculated about what the discovery of hydrogen-fueled microbes means for life on other planets.

"Hydrogen is the most abundant element in the universe," Spear points out. "If there is life elsewhere, it could be that hydrogen is its fuel."

Critters in a cold climate
Other tiny critters prefer the cold.

Hiding beneath sheets of ice in Siberia and Antarctica are microbes called psychrophiles or psychrotrophs. They consist mostly of bacteria, fungi and algae that thrive in freezing temperatures ranging from 23 to 59 degrees Fahrenheit (-5 to 20 Celsius).

In addition to being cold, the environments that these microbes are found in are sometimes at tremendous depths — more than 2 miles (3.2 kilometers) below the surface.

Psychrophiles help us clean up arctic oil spills. They also turn our milk sour. There is a good chance, scientists say, that extraterrestrial life could be similar to this class of microbes. In a solar system where many of the planets — including Mars — have large ice deposits and colder temperatures in general, psychrophiles might thrive.

Undersea hot spots
Rising as high as 15 stories off the ocean floor at depths of 7,000 feet (2,100 meters), hydrothermal vents that spew acidic, mineral-rich water are the places to be — if you can stand the heat. The water coming out of the vents can reach temperatures as high as 750 degrees Fahrenheit (400 degrees Celsius), but that’s just fine for undersea thermophiles.

The mineral-munching microbes living around these volcanic "chimneys," which are so deep no sunlight can reach them, give yet another view of what life could be like on another planet, where lack of sunlight would hinder organisms relying on photosynthesis as their energy producing mechanism.

A number of the planets and moons in our solar system are covered in ice, but scientists speculate that below some of that ice are liquid oceans. If there is also volcanic activity on those ocean floors, it is possible that similar hydrothermal vents could be growing there as well. Although it is nearly impossible to know whether there is life in those oceans, such worlds would at least contain an environment in which we know organisms could live.

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