Boreskov

MICROFOSSILS, BIOMOLECULES AND BIOMARKERS IN CARBONACEOUSMETEORITES: IMPLICATIONS TO THE ORIGIN AND EVOLUTIONOF THE BIOSPHERERichard B. Hoover 1 , Alexei Yu. Rozanov 2PL‐61 NASA/Marshall Space Flight Center, VP62, 320 Sparkman Dr., Huntsville, AL 358052 Borissiak Paleontological Institute, Russian Academy of Sciences, 117647 Moscow, RussiaWork carried out since the early 1960’s has conclusively established that pristine CI1 andCM2 carbonaceous meteorites contain indigenous and extraterrestrial biomolecules (e.g.,chiral protein amino acids, carboxylic acids, nucleobases, etc.) and biomarkers (e.g.,geologically stable diagenetic breakdown products of biomolecules such as nitrogen andsulphur heterocycles, porphyrins, pristane, phytane, cycloalkanes, polymers of isoprenes,etc.). Scanning Electron Microscopy studies in the United States and Russia have detectedlarge numbers of permineralized and carbonized filamentous microstructures embedded insituin freshly fractured interior surfaces of the meteorites. The size, size range anddistinctive morphological characteristics such as differentiated sheaths, trichomes andspecialized cells and structures for nitrogen fixation (heterocysts); survival and reproduction(hormogonia, baeocytes and akinetes) and attachment (fimbriae) demonstrate that many ofthese filaments are convergent with morphotypes of known genera of trichomiccyanobacteria and other filamentous trichomic prokaryotes. Energy Dispersive X‐RaySpectroscopy (EDS) studies have shown many of the filaments have O/C ratios consistentwith bitumen or kerogen and nitrogen content typically < 0.5%, which is far below the range(2‐18% atomic) measured under identical conditions for living cyanobacteria or dead(Holocene – Pleistocene) biological remains (hair and tissues of mummies and mammoths).These measurements exclude the interpretation of the filaments as recent terrestrial biocontaminants.Furthermore, many independent studies have shown that thesecarbonaceous meteorites do not contain unstable biomolecules that are essential to life andfound in living and recently dead organisms (e.g., 12 protein amino acids; the nucleobasesthymine and cytosine; RNA and DNA sugars ‐ ribose and deoxyribose; metabolites, enzymesand pigments ‐ NADH, ATP, chlorophyll and chlorins). This has led to the interpretation ofthe recognizable biogenic filaments found in the meteorites as indigenous microfossils thatwere present in the meteorites when they entered Earth’s atmosphere. It is suggested thatthe detection of indigenous biological remains in carbonaceous meteorites may havesignificant implications to the origin and evolution of the terrestrial biosphere.Understanding the nature and characteristics of the mineralogy and thermal and aqueousalteration of the meteorite parent body may provide useful insights to guide theoretical andexperimental investigations concerning the fundamental problem of the origin of life.15