April 16, 2009 -- Beneath a glacier in Antarctica, scientists have discovered a community of microbes growing in frigid pools of salty water.
It's a particularly tough environment, with no light, no oxygen, and extremely cold temperatures. But the microbes appear to live -- and thrive -- off a combination of iron and sulfur, according to a new study. The result of that strange metabolism is a brilliant red streak of cascading ice called Blood Falls.
"I don't know of any other place like it on Earth," said Jill Mikucki, a geomicrobiologist now at Dartmouth College in Hanover, N.H. "It's an attractive feature in a barren landscape of brown dirt, white ice and blue sky."
The new study, which appears this week in the journal Science, hints at how life might be able to exist in other inhospitable corners of the universe, such as Jupiter's moon Europa. Isolated for millions of years, the microbes under Blood Falls may also provide glimpses of previous glacial episodes in Earth's history.
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"This lake that has been trapped beneath Antarctic ice represents one of those extreme environments where life has held on under the most adverse conditions," said Jay Kaufman, a biogeochemist at the University of Maryland in College Park. "This is absolutely unique."
Blood Falls is a striking feature. Cutting through Taylor Glacier in the McMurdo Dry Valleys of Antarctica, the bright red river of ice is about 200 feet tall. Explorers discovered the falls in 1911. In the 1950s, scientists took samples of the salty red crust and discovered iron.
Only in the last few years have researchers developed an explanation for what's happening there. Millions of years ago, they suspect, seawater flooded the valley before retreating and leaving behind a salty lake. Taylor Glacier then moved over the lake, trapping the water beneath it.
Today, this salty liquid periodically oozes out from the edges of the ice, coloring it red and opening a window into the sub-glacial world. By studying the seepage, scientists can learn about that world without the same worries of contamination that make them hesitant to drill through ice into other subglacial lakes.
In previous work, Mikucki analyzed the brine from Blood Falls and found evidence of about 20 types of microbes. Models predicted the existence of another 10.
Once she knew who was there, she wanted to find out how they managed to grow. Without oxygen or light, after all, photosynthesis would be impossible. The microbes had to be doing something else. To investigate, Mikucki and colleagues collected samples of oozing liquid from the site and looked in it for the presence of various forms of oxygen, iron, sulfur and other substances.
The chemical analyses showed that the microbes breathe in a form of iron that leaches into the water from the bedrock below. Then, with the help of sulfur compounds as catalysts, the microorganisms breathe out a different form of iron, which gives Blood Falls its rusty color.
"We've never seen that type of metabolic cycle in a natural system before," Gehring said.
In a nod to their oceanic roots, genetic work showed that the microbes are closely related to marine organisms. This population has been isolated for at least 1.5 million years.
Europa, has an icy crust on top of a salty liquid sea. So it's possible that similar types of microbes live there and in other similar environments throughout the universe.
The work also provides concrete evidence, Gehring said, of how life could have endured Snowball Earth periods, which may have periodically covered the globe completely with snow and ice at various times in the planet's history, though Kaufman disputes those particular conclusions.
Either way, the research highlights the relentless resilience of life on Earth.
"Here's an ecosystem that has been covered for millions of years and has persisted below the ice," Gehring told Discovery News. "As long as there's energy, life finds a way to take advantage of it."
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Satellite Images of Blood Falls
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