Guide to the wildest life on Earth

Life in the deep ocean, in rocks ... and in space?
A sediment sample recently dredged up from Challenger Deep, the deepest part of the Pacific Ocean, was abundant in single-celled protists called foraminifera. Researchers were surprised to find these soft-shelled critters at depths of nearly 7 miles (11.2 kilometers), where the pressure is 1,100 times greater than at the surface.

"I am very surprised that so many very simple, soft-shelled foraminifera are dwelling at the deepest part of the ocean," said Hiroshi Kitazato, of the Institute for Research on Earth Evolution at the Japan Agency for Marine-Earth Science and Technology.

Kitazato suggests that the deep trenches, where the creatures can feed on bits of sunken organic matter, may provide a refuge for the foraminifera.

The fossil record of foraminifera is more than 550 million years old. In last week’s issue of the journal Science, Kitazato suggested that these new creatures probably represent the remnants of a deep-dwelling group that was able to adapt to high pressures.

The rest of the wild bunch

• It’s a hard rock life: Endoliths and hypoliths are two types of extremophiles that live inside rocks or between the mineral grains. Endoliths have been found more than 2 miles below Earth’s surface, and if they can stand the heat, they could dwell much deeper. Early observations show that they feed on surrounding iron, potassium or sulfur. Water is scarce at these depths, and this slows down the procreation cycle of the organisms — some reproduce only once every 100 years! Hypoliths are photosynthetic organisms, so the rocks they live in must be translucent, like quartz. Hypoliths are commonly found in extreme deserts in cold climates, such as Antarctica on the Canadian Arctic's Cornwallis Island. Their translucent homes provide them with many comforts, such as trapped moisture and protection from ultraviolet rays and harsh winds.
• Hot and hotter: Hyperthermophiles are organisms that prefer temperatures above 140 degrees F, some even as high as 250 degrees F (121 degrees C), although those have trouble reproducing. The hardiest of the 50 known species are those living near hydrothermal vents — these require temperatures of over 194 degrees F (90 degrees C) to live. In addition to being heat-resistant, many hyperthermophiles can withstand other environment stresses, such as high acidity and radiation. One thermophile, Thermus aquaticus, produces a DNA polymerase enzyme that is widely used in molecular biology research for use in high-temperature polymerase chain reactions used to replicate DNA.
• Mightier than a cockroach: Toxitolerant organisms can withstand high levels of damaging agents. They can be found swimming around in benzene-saturated water or in the core of a nuclear reactor. One species of bacteria, Deinococcus radiodurans, can withstand a 15,000-gray dose of radiation – 10 grays would kill a human, and it takes over 1,000 grays to kill a cockroach. Extraterrestrial life forms would most likely need to possess similar tolerances to radiation, because the atmosphere on other planets, or lack thereof, filters out much less radiation than Earth’s.
• On a diet: Oligotrophic bacteria survive in, and in some cases prefer, environments that are low in nutrients. They have evolved metabolic processes that allow them to produce their own sulfur and phosphorus, and they feed on their own organic waste.

While there is no evidence for life beyond Earth, information about extraterrestrial environments combined with the discoveries of life in places on our planet thought to be inhabitable keeps scientists optimistic.

"If it works this way on Earth, it’s likely to happen elsewhere," says Spear, the University of Colorado scientist. "When you look up at the stars, there is a lot of hydrogen in the universe."

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