Figure 1. Microfossils in the Orgueil meteorite in morphology and size consistent a Microcoleus sp. (multiple trichomes within a common sheath) and Phormidium sp. (uniseriate trichome) mat. These two genera of cyanobacteria often grow together forming mats at the bottom of ice-covered lakes and permafrost in Siberia and Antarctica. (3)

Figure 2. Cyanobacterial filaments in Orgueil meteorite with single trichome encased within a thick sheath similar to members of the Oscilliatoriacea and the well-known genus Lyngbya. The empty helical sheath provides evidence of oscillatory motility and cross-wall constrictions allow the sizes of cells within the sheath to be determined. (3)

Figure 3.Cyanobacterial filaments in the Murchison CM2 meteorite showing a Microcoleus sp. multiseriate filament (multiple trichomes within a common laminated sheath), an escaped hormogonium with cross-wall constrictions and a tapered trichome with a calyptrate apical cell. These multiple recognizable features are clearly biological and distinctive of the known features of components of cyanobacterial mats known on Earth. (3)

At the Astrobiology XIII session, 3-5 August 2010, of this year's SPIE conference in San Diego, NASA scientist Richard Hoover showed images that add weight to the case for fossilized cyanobacteria in meteorites. The fossils are found in carbonaceous meteorites of several types, including CI1 (example: Orgueil) and CM2 (example: Murchison). Here we present some typical and previously unpublished images from those meteorites.

The fossils are biological.

Chemical mapping shows that carbon and other life-critical bio-elements are distributed in the forms as appropriate for biological fossils, but the filaments are also infilled with Epsomite (hydrated magnesium sulfate), which was deposited in the hollow sheaths after the organisms died. Amino acids, nucleotides, and other life-critical biomolecules are found in the same carbonaceous meteorites that contain the fossils. The excess of L-amino acids, a property of the proteins in all living organisms known, is consistent with life — and with no known explanation by abiotic production processes (which yield equal numbers of the D- and L- forms). Clearly, the fossils found in the meteorites are biological.

Are they recent contaminants?

The Orgueil meteorite was observed to fall in France in 1864. It is one of only five extremely rare CI1 meteorites known on Earth. These very precious stones have always been carefully curated in museums in sealed containers, since it has been known since 1806 when the Alais meteorite fell that the stones rapidly disintegrate when exposed to water or to a moist atmosphere. On the other hand, some of the more substantial samples of the Murchison CM2 meteorite, which landed in Australia in 1969, were merely stored in boxes in museum drawers.

Hoover (1,2) previously described many of the indigenous microfossils in the Orgueil and Murchison meteorites in detail. He also reported one Murchison sample that had been contaminated after arrival on Earth by filamentous fungi that can grow on fairly dry substrates. The modern fungal contaminants were pale blue in color and they contained the high levels of nitrogen (2-15% atomic) found in all modern organisms. Furthermore they moved and were damaged by exposure to the Electron Beam (consistent with the responses of living or recently dead cells) of the Field Emission Scanning Electron Microscope. This was clear evidence that they were modern contaminants. However, this was the only case of fungal contamination that has been encountered since 1996 when Hoover and his collaborator, Academician Alexei Yu. Rozanov (Director of the Paleontological Institute of the Russian Academy of Sciences in Moscow) began their studies of microfossils in carbonaceous meteorites.

Elemental analysis by Energy Dispersive X-Ray Spectroscopy revealed that the permineralized cyanobacterial fossils discovered by Hoover typically had nitrogen and phosphorus levels below the EDS detection limit and carbon/nitrogen, carbon/sulfur ratios that were consistent with ancient (but not modern) biology. Furthermore, the fossils of "blue-green algae" (cyanobacteria) that Hoover discovered in these meteorites are aquatic organisms that grow only during total immersion in liquid water on Earth. If the Orgueil meteorite stones had been immersed in liquid water after landing on Earth, they would have disintegrated. Therefore, the contamination argument against them rings hollow.

The Murchison meteorite was seen as it fell in Australia in 1969. Some of the fragments were gathered immediately and were too hot to touch — others were later found with frosting on the fusion crust. This indicates that only a thin layer of fusion crust became hot and the ice cold interior remained frozen during the short time the meteorite fireball came through the upper atmosphere (similar to the blazing entrance of an Apollo capsule with the Astronauts inside). During his presentation at SPIE, Hoover pointed out that these meteorites contain not only microfossils, but chiral amino acids that are a distinctive signature of life. However, only eight of the twenty protein amino acids and three of the nucleobases needed for life are found in the meteorites. If these stones were contaminated by microorganisms after landing on Earth, then they would contain all twenty amino acids and all five nucleobases would be present and the filaments would have clearly detectable levels of nitrogen and phosphorus. He also pointed out that the amino acids that are missing from the meteorite are present in 40,000 year old Pleistocene Mammoths, but they are also missing from 65 million year old bones of Dinosaurs. He concluded that the filaments found in these meteorites provide clear and convincing proof for the existence of extraterrestrial life and support the hypothesis of an exogenous rather than an endogenous origin of Earth Life.

In both the Orgueil CI1 and the Murchison CM2 meteorites, fossils were discovered in freshly fractured interior surfaces of the samples and often embedded in the rock matrix of the meteorites. Furthermore, 2-D elemental maps of the fossils show that the chemical distributions within the fossilized filaments are distinct from those of the meteorite matrix and are consistent with ancient fossils of biological life forms but inconsistent with recent contaminants. For example, unlike recent contaminants (but like ancient fossils on Earth), they are depleted in both nitrogen and phosphorus and often have unusually high content of magnesium, sulfur and carbon.

Conclusion

Acknowledgements

13 Jun 2016

24 Apr 2012

Is there life in space?

9 Mar 2011

3 Mar 2011

24 Sep 2010

24 Aug 2010

15 Aug 2010

Search for Microfossils in Carbonaceus Chondrites

References   |   Richard Hoover: collected articles