More findings about life on the Red Planet.If Martians could look down on Earth, they might be amused. Ever since a startling report last August, Earthlings have hotly debated whether a potato-shaped meteorite contains fossil evidence of primitive life on the Red Planet.
Some of the controversy focuses on whether carbonates found in the meteorite were formed at low temperatures, in an environment hospitable to life, or at much higher temperatures. Speaking to a standing-room-only crowd last week at NASA's Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately 6.5 miles northeast of Washington, D.C. in Greenbelt, Md., David S. McKay David S. McKay is Chief Scientist for Astrobiology at the Johnson Space Center. Dr. McKay was the first author of a major scientific paper (Science, Aug. 16, 1996) postulating past life on Mars on the basis of evidence in Martian meteorite ALH84001 found in Antarctica. , a leader of last August's discovery team, disputed a recent report arguing for a high-temperature origin for material in the meteorite. He also presented new evidence that the rock, dubbed ALH ALH Advanced Light Helicopter
ALH Amplitude of Lateral Head (Displacement)
ALH Alpha Hospitality Corporation (former stock symbol; now ALHY)
ALH Advanced Liquid Hydrogen 84001, contains fossils of primitive bacteria from Mars.
McKay, of NASA's Johnson Space Center in Houston, countered criticisms that the tiny, wormlike structures thought to be microfossils in the meteorite could not, in fact, have been formed by a living organism (SN: 12/14/96, p. 380). John P. Bradley of MVA MVA
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MVA Motor vehicular/vehicle accident, see there in Norcross, Ga., and the Georgia Institute of Technology Georgia Institute of Technology, in Atlanta, Ga.; coeducational; state supported; chartered 1885, opened 1888. It is a member school in the university system of Georgia. Significant among its facilities and programs are the Frank H. in Atlanta and his colleagues had reported evidence that the apparent microfossils in ALH84001 are elongated e·lon·gate
tr. & intr.v. e·lon·gat·ed, e·lon·gat·ing, e·lon·gates
To make or grow longer.
adj. or elongated
1. Made longer; extended.
2. Having more length than width; slender. , whiskerlike crystals of magnetite.
The whiskerlike shape has been associated with high-temperature activity, which cannot support water-based life, near volcanic vents. Bradley and his colleagues also found that some of the magnetite crystals contain structural defects that are not known to be produced in a biological environment. One of them, a spiral defect, typically occurs when atoms crystallize from a high-temperature vapor. In the other defect, known as twinning, atomic lattices that are mirror images of each other join at a common boundary.
Although McKay continues to assert that his team has not seen the whiskerlike shapes or the defects in microfossils from ALH84001, he also cites two older reports, previously overlooked, demonstrating that tiny bacteria can produce both whiskers and twinning.
"Two out of three of [Bradley's] arguments are completely out the window," asserts Joseph L. Kirschvink of the California Institute of Technology California Institute of Technology, at Pasadena, Calif.; originally for men, became coeducational in 1970; founded 1891 as Throop Polytechnic Institute; called Throop College of Technology, 1913–20. in Pasadena. Bradley notes, however, that McKay's team had originally claimed that the apparent microfossils were and should be flawless if they were produced by living material. No one has yet demonstrated that bacteria can produce the spiral defect, he adds.
During his talk, McKay displayed intriguing micrographs that show what appear to be filmy coatings around carbonate globules in the meteorite. McKay suggests that the coatings, which survived even after the carbonates were etched away by acid or ions, are either a clay mineral or a protective, biological layer known as a biofilm Biofilm
An adhesive substance, the glycocalyx, and the bacterial community which it envelops at the interface of a liquid and a surface. When a liquid is in contact with an inert surface, any bacteria within the liquid are attracted to the surface and adhere . Modern colonies of bacteria can produce biofilms.
In a report to be given in March at the annual Lunar and Planetary Science Conference The Lunar and Planetary Science Conference (LPSC), jointly sponsored by the Lunar and Planetary Institute (LPI) and NASA Johnson Space Center (JSC), brings together international specialists in petrology, geochemistry, geophysics, and astronomy to present the latest results of in Houston and already posted on the Internet, Kirschvink's team argues that ALH84001 hasn't been heated to more than 110#161#C since 4 billion years ago, long before any bacteria could have infiltrated the rock. The researchers found that two tiny, adjacent pieces of the meteorite showed dramatically different responses to an applied magnetic field. Exposure to high temperatures would have erased any such differences, they assert.
These results also provide a hint that ancient Mars had a magnetic field. That's good news for proponents of life on Mars Scientists have long speculated about the possibility of life on Mars owing to the planet's proximity and similarity to Earth. It remains an open question whether life exists on Mars now, or existed there in the past. , because the field would have steered away charged particles, belonging to the solar wind, that would otherwise have eroded the planet's atmosphere. An eroding atmosphere, with its large climate variations, could have proved catastrophic for life on the Red Planet.