A Rusty old world could solve mystery of iron oxidation on Earth
Scientists have been debating for a century whether iron oxide, commonly known as rust, results from biological or inorganic processes. The question of whether life forms such as bacteria or viruses play a role in the formation of rocks rich in iron oxide has not yet been settled, Folk said.
But Folk and Milliken say the microscopic shapes they found would strongly suggest that living matter is intimately involved in the process. Their findings will be presented at the Geological Society of America meeting on Wednesday (March 22) in Charleston, S.C. Milliken is a research scientist in the department of geological sciences.
Folk is a Dave P. Carlton Centennial Professor Emeritus in Geology in the department, who has done pioneering work on forms called nannobacteria. Nannobacteria are incredibly small strands, along with spherical and egg-shaped objects found in rocks and minerals and believed by a few scientists to be dwarf forms of bacteria. They are about 1,000 times smaller than normal bacteria. Folk said half a billion nannobacterial cells could fit on a pinhead.
Many biologists say no living creature could be smaller than about 0.2 microns because they say that is too small a size to contain the genetic material necessary for life. (A micron is one-millionth of a meter in the metric system.) And other scientists deny the structures represent the presence of life, arguing that the suggestive shapes are merely the result of chemical actions or weathering.
Folk and other researchers admit that suspiciously lifelike shape does not necessarily prove or disprove the presence of life. But they believe the forms are fossils of the most primitive and earliest life forms on found on Earth and beyond.
Folk discovered the first mineralized nannobacteria in an Italian hot springs deposit about 10 years ago. Folk's nannobacteria web page contains a photo gallery of the mysterious shapes found in fossil form in mineral and rock samples from Italy and from carbonaceous meteorites. The address is http://www.geo.utexas.edu/Illite/ .
Folk and Milliken's most recent research shows that modern iron oxide deposits (rust) contain these same tiny filamentous structures shaped like very small microbes. The iron oxides also contain a veritable "zoo" of other nano-sized bodies, which Folk said indicate the presence of life.
Folk found the same features in both the new forms and the ancient forms of the iron deposits. "Together we worked on iron oxides ranging from those that clog present-day pipes to ancient iron deposits as old as three billion years," Folk said. Folk said in modern oxides "these nano-scale features are clearly organic because they remain in residue after iron oxides have been leached out. Bacteria and nannobacteria leave abundant evidence of their presence in iron oxides in the shapes we see under the microscopes."
The scientists used a simple new technique to separate out the nannobacteria. "Slightly dissolving iron oxide with hydrochloric acid reveals the entombed nannobacteria -- a method that has not heretofore been used, nor has investigation of the deposits been made at such high magnifications," Folk said. "These dwarf forms of bacteria precipitate the iron oxide in modern rust. The presence of these same forms in ironrich sediments that are extremely ancient (billions of years) indicates their important role in chemical reactions."
Normal-sized iron bacterial filaments are seen best with a 3-D microscope. Very minute nannobacterial cells -- cells 50-to-100 nanometers in diameter -- are visible only using an electron microscope. These features are easily found in iron oxides of all ages in rocks on Earth by using the new microscope technology. If the research is correct, Folk said the same methods could be useful in evaluation of iron-rich rocks that eventually may be retrieved by Martian exploration vehicles.
When NASA scientists in 1996 announced that odd formations, resembling terrestrial nannobacteria, appeared to be present in a carbonate vein of a 4.57 billion-year-old Martian meteorite recovered in Antarctica some years earlier, they based their announcement on Folk's research on Italian travertines (a type of limestone). Folk said his work on the other carbon- bearing meteorites "implies that minute forms of life may have existed not only on Mars but also on other planets and asteroids, the source of most meteorites."
Folk and his nannobacteria research team include Dr. Brenda L. Kirkland of the UT Austin department of geological sciences, Dr. Leo Lynch of the Mississippi State University department of geosciences, Dr. Ian J. Molineux, a professor in the UT Austin department of molecular genetics and microbiology and Dr. Robert J.C. McLean of the Southwest Texas State University biology department.
Water + Energy = Life?
Pasadena - March 9, 2000 - Life on Earth is not necessarily the best analogy for life on another world. In other words, astrobiologists should be prepared to use chemistry and physics to analyze the possibilities for extraterrestrial life, rather than merely assuming life will exist wherever there is water.