NASA Announces New Evidence Regarding Past Life on Mars
Updated: 27 Feb 2001 2:30 PM EST
Today, a team of NASA scientists is announcing that they have determined that small magnetite crystals in the now-famous ALH84001 Martian meteorite were almost certainly produced by living organisms – organisms that must have lived on Mars. The results of this research will be published in the 27 February 2001 issue of the Proceedings of the National Academy of Sciences.
The ALH84001 meteorite is the same sample wherein scientists at NASA’s Johnson Space Center in Houston first announced in 1996 that they had found evidence of possible past life on Mars. This meteorite was blown off of Mars millions of years ago by a large impact event and circled the sun until hitting the Earth 13,000 years ago. It then lay undisturbed in near-pristine condition in the Antarctic until collected by meteorite hunters.
The rock itself was formed on Mars early in its history – almost 4 billion years ago. The fossils that NASA scientists claim to have found within the rock are thought to have been left long after the rock was initially formed when Martian organisms entered through cracks in its structure and then died.
Analysis of this meteorite’s mineralogy and trapped gases were virtually identical to geologic and atmospheric data sent back by the Viking landers – leading to the conclusion that it was a piece of Mars. A dozen or so meteorites have been found around the world which are also thought to have been blasted off of Mars.
Among the lines of evidence cited by Drs. Kathie Thomas-Keprta, David McKay, and Everett Gibson from Johnson Space Center to support their original claim that small structures found within the meteorite are fossils is the presence of small crystals of magnetic material called “magnetite”. The magnetite crystals found in the ALH84001 meteorite are very similar to those produced by magnetotactic bacteria found on Earth. Magnetotactic bacteria use these crystals (which are actually small magnets) to orient themselves with respect to Earth’s magnetic field.
Now, a research team led by Dr. Imre Friedmann at NASA’s Ames Research Center has provided additional evidence supporting the view that these crystals could only have been formed by living organisms. While the Houston team looked at individual crystals, Friedmann’s team examined how the crystals are arranged in groups. The found that the structure and arrangement of the crystals to be very similar to the way that magnetite crystals are arranged within terrestrial magnetotactic bacteria. The neatly ordered chain-like arrangement observed by Friedmann’s team is not seen in groups magnetite crystals created by non-biological means.
In his paper, “Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin”, Friedemann et al address an issue that had caused some scientists to wonder whether magnetite particles found in the ALH84001 were from living organisms: the apparent lack of organized chain structures characteristic of the magnetite particles found in terrestrial magnetotactic bacteria. Friedmann report that: “Five characteristics of such chains (uniform crystal size and shape within chains, gaps between crystals, orientation of elongated crystals along the chain axis, flexibility of chains, and a halo that is a possible remnant of a membrane around chains), observed or inferred to be present in magnetotactic bacteria but incompatible with a nonbiological origin, are shown to be present.”
Over the past four years, the NASA JSC team has prepared multiple reports comparing the shape and composition of the magnetite crystals found in association with putative microbial fossils in ALH84001 with similarly shaped and sized crystals of magnetite formed by terrestrial bacteria. Friedmann et al weigh in on this issue as well.
According to another paper in the same issue of this journal “Truncated Hexaoctahedral Magnetite Crystals in ALH84001: Presumptive Biosignatures,” published in the Proceedings of the National Academy of Sciences Friedmann et al state that “We have characterized a subpopulation of magnetite (Fe3O4) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1.”
The basis for these findings has to do with the shape of these crystals and the fact that no one has yet to decribe a non-biological way to produce them:
“Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection.”
It is important to note that members of Friedmann’s research team include scientists such as Dennis Bazylinski and Joseph Kirschvink who have been studying magentotactic bacteria for decades. As such it is rather notable that they would co-author a paper that states: “Unless there is an
unknown and unexplained inorganic process on Mars that is
conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet
found.”
According to Kirschvink “The process of evolution has driven these bacteria to make perfect little bar magnets, which differ strikingly from anything found outside of biology. In fact, an entire industry devoted to making small magnetic particles for magnetic tapes and computer disk drives has tried and failed for the past 50 years to find a way to make similar particles. A good fossil is something that is difficult to make inorganically, and these magnetosomes are very good fossils.”
In a second paper in the same journal, “Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin”, Friedemann addresses an issue that had caused some scientists to wonder whether magnetite particles found in the ALH84001 were from living organisms: the lack of organized chain strctures found in terrstrial magentotactic bacteria. Friedmann et al respond that: “Five characteristics of such chains (uniform crystal size and shape within chains, gaps between crystals, orientation of elongated crystals along the chain axis, flexibility of chains, and a halo that is a possible remnant of a membrane around chains), observed or inferred to be present in magnetotactic bacteria but incompatible with a nonbiological origin, are shown to be present.”
The evidence that Thomas-Keprta and her team provide to support their claim that the ALH84001 meteorite contains evidence of past life on Mars is not limited to the study of magnetite crystals. Instead, they present data from a series of parallel and overlapping analyses which together (they claim) point to a biological answer as being the best way to explain the features they have found within this piece of Mars.
In years since their public announcement in August 1996, Thomas-Keprta and her colleagues have provided a steady stream of data regarding the nature of carbonate materials found within the meteorite and how their formation is best explained as being the result of the low temperatures associated with biological processes; how the shape of small fossilized structures found associated with the carbonates (and the magnetite crystals) are similar to how bacteria become fossilized on Earth; and the fact that the location of all of these features within the rock was more or less isolated from the possibility of terrestrial contamination.
“Until now, studying life has been like trying to draw a curve using only one data point — life on Earth,” said Imre Friedmann. “Now we have two data points to draw life’s curve.” The next step is to find the remains of the bacteria themselves, he said.
While all of these findings are exciting to some, there are scientists who feel that some or all of the lines of evidence that NASA’s researchers have presented can also be explained by non-biological process – or possibly by terrestrial contamination.
The only way we’ll know for certain whether Mars ever had life is to go there and look for ourselves.
Related Links
° 27 February 2001: Truncated Hexaoctahedral Magnetite Crystals in ALH84001: Presumptive Biosignatures, Proceedings of the National Academy of Sciences [abstract – subscription required for access to full article]
° 27 February 2001: Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin, Proceedings of the National Academy of Sciences [abstract – subscription required for access to full article]
° 26 February 2001: Photographic Comparison of Terrestrial and Martian Magnetite Crystal Chains, NASA ARC
° 26 February 2001: New Evidence Strengthens Claims of Ancient Life on Mars – Study of Martian Meteorite Reveals Magentic Fossils, NASA JSC
° 26 February 2001: NASA JSC Background Information on PNAS ALH84001 Magenetite Paper, NASA JSC
° 26 February 2001: Case For Life on Mars Withstands Criticism, Gains Scientific Support, NASA JSC
° 26 February 2001: Scientists Finds Evidence of Ancient Microbial Life on Mars, NASA ARC
° 26 February 2001: NSF official describes hunt for antarctic meteorites related to new meteorite evidence of primitive life on Mars, NSF
Background Information
° 12 December 2000: New report links meteorite to possibility that microscopic life existed on Mars, NSF
° 1 August 2000: British Researchers Try to Challenge Evidence of Mars Meteorite Fossils – But Don’t Make Their Case, SpaceRef
° 16 August 1996: Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 , D. S. McKay, E. K. Gibson Jr., K. L. Thomas-Keprta, H. Vali, C. S. Romanek, S. J. Clemett, X. D. F. Chillier, C. R. Maechling, R. N. Zare, Science, Volume 273, Number 5277
° Mars May Be Even Wetter Than It Was Last Week, SpaceRef
° It’s dead Jim. But was it ever alive? The ALH84001 announcement at T+2 years, Ad Astra Magazine
° Meteorites from Mars!, NASA JSC
° Meteorites From Mars, Whole Mars Catalog
