Extremophiles: Amazing Microbial Survivors
Some live in airless seams of burning rock; (61)miles beneath Earth’s surface and around the hydrothermal vents of deep-sea volcanoes. Others, salt-encrusted, “sleep” in ancient caverns, waking (62)after centuries to feed and to be bred. (63)Radioactive pools of toxic waste are okay for others to live in; (64)even acid cannot kill them. In lightless vacuums and locales once thought to hot, to cold or to poisonous, (65)to sustain life, there exists a wealth of microbial organisms. These single-celled survivors called extremophiles, (66)don’t merely endure environments too severe for other life forms; they (67)thrive in them.
Heat-loving extremophiles, or thermophiles, flourished (68)in temperatures over 150 degrees Celsius. Scientists have collected them from the Yellowstone National Park’s thermal pools, the park abounding with geysers like Old Faithful, (69) and from radioactive rock deep within South African gold mines.
In the hot waters surrounding Juan de Fuca Ridge in the Pacific Ocean, thermophiles ensure the survival of other marine life. (70) Here, the ocean floor is scarred by earthquakes and underwater volcanoes.(71)Poisonous waters from cracks (72)at temperatures up to 360 degrees Celsius gush in the ocean floor, and thermophiles convert the toxic chemicals into food for crabs, giant worms, and other deep-sea life.
Psychrophiles live in harsh and inhospitable places on our planet. (73)One ancient breed of psychrophile lives in million-year-old ice miles below an Antarctic glacier. In the ice of the South Pole, psychrophiles survive not only darkness and subzero temperatures but also ultraviolet radiation.
If life can persist in extreme environments on Earth, scientists speculate that life may endure under similar conditions elsewhere, perhaps in the frozen seas or the exploding volcanoes of Jupiter’s moons, or beneath the barren landscape of Mars.(74) Nevertheless, (75)findings suggest that life—at least on the microbial level—may flourish throughout the universe in places we have yet to look.
73. Given that all the choices are true, which one would LEAST effectively introduce the subject of Paragraph 4?
A. NO CHANGE
B. According to researchers, the environment of a cold-loving extremophile, or psychrophile, is as extreme as that of a heat-loving thermophile.
C. Certain extremophiles, called psychrophiles, thrive in cold environments rather than hot ones.
D. Other types of extremophiles—cold-loving psychrophiles—have been found in temperatures as low as –17 degrees Celsius