NASA exobiology researchers confirmed Earth's oceans were once richin sulfides that would prevent advanced life forms, such as fish andmammals, from thriving. The research was funded in part by NASA'sexobiology program.
A team of scientists from the Massachusetts Institute of Technologyand Harvard University, working with colleagues from Australia and theUnited Kingdom, analyzed the fossilized remains of photosyntheticpigments preserved in 1.6 billion-year-old rocks from the McArthurBasin in Northern Australia.
They found evidence of photosynthetic bacteria that require sulfidesand sunlight to live. Known as purple and green sulfur bacteria becauseof their respective pigment colorations, these single-celled microbescan only live in environments where they simultaneously have access tosulfides and sunlight.
The researchers also found very low amounts of the fossilizedremains of algae and oxygen-producing cyanobacteria. The relativescarcity of these organisms is due to poisoning by large amounts ofsulfide.
"This work suggests Earth's oceans may have been hostile to animaland plant life until relatively recently," said Dr. Carl Pilcher,NASA's senior scientist for astrobiology. "If so, this would haveprofound implications for the evolution of modern life."
"The discovery of the fossilized pigments of purple sulfur bacteriais totally new and unexpected. Because they need fairly high intensitysunlight, it means the pink bacteria, along with their essential sourceof sulfide, close to the surface, perhaps as close as 20 to 40 meters,"said Roger Summons, Massachusetts Institute of Technology professor ofgeobiology. "The sulfide would have come from bacteria that reducessulfate carried into the oceans by the weathering of rocks."
"The McArthur Basin rocks were deposited over a very large area andover many millions of years, so it's likely they formed under waterthat was intermittently connected to or actually part of an ocean. Inturn, this implies the ocean had an abundant and continuous supply ofhydrogen sulfide and must have been quite toxic to any oxygen-breathingorganisms," said team member Jochen Brocks. "In fact, for seven-eighthsof Earth's 4.5 billion-year history, there was probably little oxygenin the oceans and certainly not enough to support oxygen-breathingmarine animals."
This research continued the efforts of NASA and partner institutionsto understand the early history of the Earth. Research results werepublished in the Oct. 6, 2005, edition of Nature magazine.
The research was conducted by a team working in Summons' laboratory.Team members include Jochen Brocks, formerly of Harvard and now atAustralian National University; Gordon Love, Massachusetts Institute ofTechnology; Stephen Bowden, University of Aberdeen, Scotland; GrahamLogan, Geoscience Australia; and Andrew Knoll, Harvard.
For electronic images and more information about this research on the Web, visit:
http://eaps.mit.edu/geobiology/research/Ancient_bacteria.htmlFor more information about NASA's astrobiology program on the Web, visit:
http://www.astrobiology.arc.nasa.govFor more information about NASA and agency programs on the Web visit:
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