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4273-35 Evidence
for Biomarkers and Microfossils in by Richard B. Hoover and Alexei Yu. Rozanov
Abstract The detection by McKay et al.1 of chemical biomarkers and
possible microfossils in the ancient Mars meteorite (ALH84001) enhanced
interest in the possibility of microbial life on other bodies of the Solar
System and triggered the development of the rapidly emerging field of
Astrobiology. Astrobiologists are now seeking to develop conclusive
methods to recognize biomarkers and bacterial microfossils as well as
understand the spatial, temporal, environmental and chemical limitations
of microbial extremophiles. Seeking additional evidence of possible
microfossils in ancient terrestrial rocks and meteorites, independent (and
later collaborative) investigations were carried out in the United States and
Russia using the SEM, Environmental Scanning Electron Microscope (ESEM),
and Field Emission Scanning Electron Microscope (FESEM). In-situ
investigations of freshly broken carbonaceous chondrites have shown the presence
of a large number of complex microstructures that appear to be lithified
microbial forms. Many of the forms we have found in carbonaceous
meteorites are much larger than the possible nannofossils reported from the
Allen Hills meteorite. Energy Dispersive Spectroscopy (EDS) and Link
microprobe analysis shows the possible microfossils have a distribution of
chemical elements characteristic of the meteorite rock matrix, although
many exhibit a superimposed carbon enhancement. The mineralized bodies
encountered embedded in the rock matrix of freshly fractured meteoritic
surfaces can not be easily dismissed as recent surface contaminants.
Many of the forms found in-situ in the Murchison, Efremovka, and Orgueil
carbonaceous meteorites are strikingly similar to microfossils of coccoid
bacteria, cyanobacteria and fungi such as we have found in the Cambrian
phosphorites of Khubsugul, Mongolia and high carbon Phanerozoic and Precambrian
rocks of the Siberian and Russian Platforms. This paper presents SEM
images of microfossils that exhibit the characteristics of distinct stages of
microbial life cycles of Nostocacean cyanobacteria (including trichomes,
spores, and hormogonia) and ecological systems similar to those found in
permafrost and cryoconite communities of Antarctica and Siberia. Keywords Biomarkers, Meteorites, Carbonaceous Chondrites; Astrobiology; Extremophiles, Microfossils.
Principal Author Biography Richard B. Hoover is President of SPIE-The International Society
for Optical Engineering. He is Astrobiology Group Leader in the Space
Science Department of the NASA Marshall Space Flight Center. His previous
research involved the development of X-ray Microscopes and Telescopes using
normal incidence multilayer x-ray mirrors. During the past three decades,
he has conducted extensive investigations of microorganisms and siliceous
microfossils. Richard Hoover is Internationally known for his work on
diatoms. At the invitation of the Royal Zoological Society of Antwerp,
Belgium, he conducted the Inventory of the diatom collections of the Henri van
Heurck Museum. He has written numerous articles and books on diatoms and
micropaleontology. His diatom photomicrographs and micromounts were
exhibited at the Smithsonian Museum of Natural History and his article
"Those Marvelous Myriad Diatoms" appeared in National Geographic in
June, 1979. As a Co-Investigator in the NASA Astrobiology Institute, he
has studied morphological biomarkers and microfossils in ancient rocks and
meteorites. In January, 2000, Richard Hoover served as Scientific Team
Leader of the Antarctica 2000 Expedition to collect meteorites and
microorganisms from the blue ice in the Thiel Mountains of Antarctica and snow
from the South Pole. He collected permafrost microbiota from Alaska and
Siberia and has investigated ancient microbiota cryopreserved in deep-ice cores
from Vostok, Antarctica. Principal Author Affiliation Astrobiology Group Leader
Secondary Author Affiliation Director, Paleontological Institute,
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