ORIGIN AND EVOLUTION OF VERY EARLY SEQUENCE MOTIFS IN ENZYMES

HERRICK BALTSCHEFFSKY, BENGT PERSSON#, ANDERS SCHULTZ, JOSÉ R. PÉREZ-CASTIÑEIRA* and MARGARETA BALTSCHEFFSKY
Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, S-106 91 Stockholm, Sweden, # IFM Bioinformatics, Linköping University, S-581 83 Linköping and Centre for Genomics and Bioinformatics, Karolinska Institutet, S-171 77 Stockholm, Sweden, *Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, Sevilla, Spain
e-mail: herrick@dbb.su.se

ABSTRACT
Conserved amino acid sequence motifs in enzymes often indicate involvement in the binding of metal ion(s) and/or in the binding and/or reactions of substrate(s). The four very early proteinaceous amino acids are glycine (G), alanine (A), aspartic acid (D) and valine (V) (Eigen and Schuster, 1979, The Hypercycle, Springer, Berlin). Aspartic acid stands out as the unique very early amino acid containing an additional, highly reactive free charge, suitable i. a. for cation binding. Active site motifs, that are rich in any or all of these four amino acids, may well be of early evolutionary significance.

Some "early" proteins appear to harbour or reflect very early sequence motifs. For example, certain enzymes involved in PPi metabolism, as well as in that of ATP, seem to be of great significance in this connection. Special attention has recently been given to the integrally membrane-bound, proton-pumping PPi synthase, which in bacterial photophosphorylation is the first and still only known alternative to the ubiquitous ATP synthase in biological electron transport coupled phosphorylation (Baltscheffsky et al. (1998) FEBS Lett. 457, 527-533). The putative active site of the PPi synthase has two nonapeptidyl sequences (DVGADLVGK and DNVGDNVGD), which are strongly conserved in the homologous enzyme family, which furthermore contain unusually many very early amino acids and which importantly have charged amino acids regularly arranged in positions 1, 5 and 9, five of these six being aspartic acid. Similar very early motifs are found in some other PPi metabolizing enzymes, and also, more or less similar, in some ATP metabolizing enzymes.

Based on plausible early motif evolution and also on results from both biochemical and geological investigations, emphasizing the emergence of selected homopolymers as probably being significant intermediate stages between monomers and heteropolymers in connection with the origin of life, a tentative, detailed outline of a stepwise molecular origin and evolution of biological energy conversion, with particular emphasis on its early phosphate metabolism, will be presented.

EANA, THE EUROPEAN EXO/ASTROBIOLOGYNETWORK ASSOCIATION

André Brack, President
Centre de biophysique moléculaire, CNRS, brack@cnrs-orleans.fr

ABSTRACT
The European Exo/Astrobiology Network Association, EANA, was created to co-ordinate the different European centres of excellence in exo/astrobiology or related fields already organised in national networks. The specific objectives of EANA are :
- to bring together European researchers interested in exo/astrobiology programmes and to foster their cooperation
- to attract young scientists to this quickly evolving, interdisciplinary field of research
- to create a website establishing a database of expertise in different aspects of exo/astrobiology
- to interface the Network with European bodies such as ESA, ESF, the European Commission and with non European institutions active in the field
- to popularise exo/astrobiology to the public and to students.

EANA is run by an Executive Council consisting of national members presently representing 12 European nations active in the field (Austria, Belgium, Denmark, France, Germany, Italy, Portugal, Spain, Sweden, Switzerland, The Netherlands, United Kingdom) on the basis of one representative per nation, and elected members in a number equal to the number of active nations.
EANA is affiliated to the NASA Astrobiology Institute. The formal affiliation was signed in 2002 at the Graz Workshop by Rosalind Grymes, Deputy Director of NAI, during a reception hosted by the Governor of Styria in the historical Eggenberg Castle.
EANA is member of the International Astrobiology Circle, IAC, including the Australian Centre for Astrobiology (ACA), the Spanish Centro de Astrobiologia (CAB), the French Groupement de Recherche en Exobiologie (GDR Exobio), the American NASA Astrobiology Institute (NAI), and the United Kingdom Astrobiology Forum (UKAF). The IAC has been implemented to facilitate international exchange between established bodies dedicated to astrobiology and to harmonise the planning of joint astrobiology meetings.

Collaborative researches are developed in the different fields covered by exo/astrobiology:
- Terrestrial life as a reference (Origins of life, environmental context, ingredients for primitive life, life in a test tube, diversity of bacterial life, life in the extremes, panspermia)
- Exploring the Solar System (Mars, Europa, Titan, Comets)
- Search for life beyond the Solar System (exoplanets, Corot and Darwin missions)

The First European Exo/Astrobiology Workshop held in Frascati, 21-23 May 2001, was attended by 200 scientists. The national and international activities in Exo/Astrobiology were presented, as well as the European achievements in the different fields covered by Exo/Astrobiology. Plenary, splinter and poster sessions cemented the European community.
The Second European Workshop on Exo/Astrobiology was organised in Graz, Austria, September 16-19, 2002. The workshop, attended by 320 participants, was oriented particularly to the planetology aspects of exo/astrobiology, in acknowledgement of the expertise of the local organisers.
Third European Exo/Astrobiology Workshop (in preparation), will be hosted by the Centro de Astrobiologia in Madrid, November 18-20, 2003.
The EANA Web Page is under construction. It will be hosted as part of the ESA pilot Virtual Institute at ESA/ESTEC in Noordwijk, The Netherlands.

SEARCH FOR LIFE ON MARS:
THE BEAGLE 2 LANDER AND THE STONE EXPERIMENT

André Brack
Centre de biophysique moléculaire, CNRS, brack@cnrs-orleans.fr

ABSTRACT
The search for traces of life on Mars encompasses a large number of disciplines (Brack et al., 1999; Westall et al., 2000). Beagle-2, the exobiology lander of ESA 2003 Mars Express mission, comprises an integrated suite of instruments to optimize the search for evidence of life on Mars in subsurface and rock interior samples. The package includes instruments to study sample mineralogy (composition, macroscopic and microscopic structural and textural features), organics (elemental, molecular), oxidation state and petrology (major and minor element composition). Environmental characteristics will also be measured (atmosphere, radiation budget, temperature, pressure, wind speed and direction, humidity, dust activity). The material will be sampled from protected sites (subsurface and rock interiors) with a mole and a small surface rock grinder and corer mounted on a robotic arm (Sims et al., 1999). The solid sample (soil or rock) will be heated in steps of increasing temperature, each increment being supplied with freshly generated oxygen. Any carbon compound present will burn to give carbon dioxide. The gas generated at each temperature will be analysed by the mass spectrometer. The instrument can distinguish between the two stable isotopes of the carbon and quantify the ratio. Other gases can be analysed by the same instrument including methane.
The 'STONE' experiment, flown by ESA, was designed to test whether Martian sedimentary material could survive terrestrial atmospheric entry. A basalt (inflight control), a dolomite (sedimentary rock) and artificial Martian regolith were embedded into the ablative heat shield of Foton 12, which was launched on September 1999. The collected entry samples have been analysed for their chemistry, mineralogy and isotopic compositions by a European consortium. Modifications due to atmospheric infall were tested by reference to the untreated samples. The dolomite sample was retrieved intact, although reduced to a depth of about 30% of its original thickness, suggesting that some Martian sediments could, in part, survive terrestrial atmospheric entry from space. Some kinetic isotopic fractionation accompanied the thermal degradation of the dolomite during re-entry, as evidenced by bulk isotopic measurements on different zones of the residual carbonate. The silica 'fusion crust' from the associated sample holder exhibited a significant degree of isotopic exchange with atmospheric oxygen during re-entry (Brack et al., 2002).

References

Brack, A., Fitton, B., Raulin, F. (1999). Exobiology in the Solar System and the search for life on Mars, ESA Special Publication SP 1231.
Brack, A., Baglioni, P., Borruat, G., Brandstätter, F., Demets, R., Edwards, H.G.M., Genge, M., Kurat, G., Miller, M.F., Newton, E.M., Pillinger, C.T., Roten, C.-A. and Wäsch, E. (2002). Do meteoroids of sedimentary origin survive terrestrial atmospheric entry? The ESA artificial meteorite experiment STONE, Planet. Space Science, in press.
Sims, M.R., Pillinger, C.T., Brack, A. and 26 co-auteurs (1999). Beagle 2 : a proposed exobiology lander for ESA'S 2003 Mars Express Mission, Adv. Space Res. 23, No. 11, 1925-1928.
Westall, F., Brack, A., Hofmann, B., Horneck, G., Kurat, G., Maxwell, J., Ori, G.G., Pillinger, C., Raulin, F., Thomas, N., Fitton, F., Clancy, P., Prieur, D., Vassaux, D. (2000). An ESA study for the search for life on Mars Planet. Space Sci. 48, 181-202.

EVOLUTION OF INTELLIGENT BEHAVIOR: IS IT JUST A QUESTION OF TIME?

Julian Chela-Flores
The Abdus Salam International Centre for Theoretical Physics
Strada Costiera 11; 34014 Trieste, Italy and
Instituto de Estudios Avanzados,
Caracas 1015A, Venezuela.

ABSTRACT
Two issues have been discussed in the past regarding the nature of biology in a universal context: (1) life may be a cosmic imperative (De Duve, 1995); (2) multicellular life may be a rare phenomenon in the cosmos, although the existence of microbial life may still be widespread (the 'Rare-Earth' hypothesis, Ward and Brownlee, 2000; Ward, 2003). We shall discuss a third issue: (3) evolution of intelligent behavior may be just a question of time (and preservation of steady planetary conditions), and hence ubiquitous in the universe. We will suggest an experimental approach to the earliest stages of the evolution of intelligent behavior. Widespread intelligence in the universe has far-reaching implications, even in the frontier with the humanities (Aretxaga, 2003; Vicuña, R. and Serani-Merlo, A., 2003). Darwin's theory of evolution is assumed to be the only theory that can adequately account for the phenomena that we associate with life anywhere in the universe (Dawkins, 1983). We argue in favor of the inevitability of the origin and evolution of life by assuming that Darwinian evolution is a universal process and that the role of contingency has to be seen beyond the restricted context of parallelism and evolutionary convergence (Akindahunsi and Chela-Flores, 2003), not only in biology, but also in other realms of science, such as in the early stages (high red-shift) of the evolution of the universe itself (Vladilio, 2003). Finally, we suggest that in the Europan Ocean, or possibly on the icy shell itself, we are presented with the problem of deciding whether some feasible experiments may throw some light on the deeper question of the eventual evolution of intelligent behavior elsewhere in the universe. We comment on some possible biosignatures of biochemical nature (Bhattacherjee and Chela-Flores, 2003) and discuss some possible ways of testing evolutionary biosignatures on or beneath the icy shell of Europa (Chela-Flores, 2003; Gatta and Chela-Flores, 2003).


References
Akindahunsi, A. A. and Chela-Flores, J. (2003) On the question of convergent evolution in biochemistry, in this volume.

Aretxaga, R. (2003) Astrobiology and biocentrism, in this volume.

Bhattacherjee, A. B and Chela-Flores, J. (2003) Search for bacterial waste as a possible signature of life on Europa, in this volume.

Chela-Flores, J. (2003) Testing Evolutionary Convergence on Europa. International Journal of Astrobiology (Cambridge University Press), in press.

Dawkins, R. (1983) Universal Darwinism, in Evolution from molecules to men, Bendall, D.S. (ed.),London, Cambridge University Press, pp. 403-425.

De Duve, C. (1995) Vital Dust. Life as a cosmic imperative, New York, Basic Books, A Division of HarperCollins Publishers, pp. 296-297.

Gatta, R. and Chela-Flores, J. (2003) Application of molecular biology techniques in astrobiology, in this volume.

Vicuña, R. and Serani-Merlo, A. (2003) Chance or Design in the Origin of Living Beings An epistemological point of view, in this volume.

Vladilio, G. (2003) Interstellar dust as a tracer of environments favourable to planet formation: evidence for the existence of a metallicity threshold, in this volume.

Ward, P.D. (2003) Factors leading to the appearance and survival of metazoan equivalents on habitable planets, in this volume.

Ward, P.D. and Brownlee, D. (2000) Rare Earth: Why Complex Life is Uncommon in the Universe. Copernicus, New York.

SEARCH FOR WATER OUTSIDE THE SOLAR SYSTEM

Cristiano Cosmovici
Istituto di Fisica dello Spazio Interplanetario
CNR,Roma,Italy
cosmo@ifsi.rm.cnr.it

ABSTRACT
Since the first discovery of a Jupiter-mass exoplanet in 1995, a total of 101 planetary systems with 116 planets (July 2003) are known to exist around main sequence stars. Most of the detections are based on the radial velocity method which involves the measurement of the wobbling of the stars induced by the gravitational field of the orbiting giant planets. No information can be thus derived on the chemical composition of the planetary atmospheres and on the existence of terrestrial-type planets where life may evolve. The ITASEL programme (Italian Search for Extraterrestrial Life) started in 1994 after the discovery of the first water emission in the atmosphere of Jupiter induced by a cometary impact (Cosmovici et al, 1996). Our measurements have shown that the water maser line at 22 GHz can be used as a powerful diagnostic tool for planetary search outside the solar system, as comets are able to deliver very large amounts of water to planets raising the fascinating possibility of extraterrestrial life evolution. In 1999 we started the search for water in 17 different targets up to 50 light years away from the Sun by using a new developed fast multichannel spectrometer, coupled to the 32 meter dish of the Medicina radiotelescope, near Bologna, Italy. Here we report the possible detection of water emission in the atmospheres of planets orbiting Ups And, 47 CMa and Eps Eri and the work to be carried out in order to confirm and extend the discovery.

Reference
1) Cosmovici, C.B., Montebugnoli, S., Orfei, A., Pogrebenko, S. and Colom, P. (1996) "First evidence of planetary water maser emission induced by the Comet/Jupiter catastrophic impact, Planet. Space Sci, 44, 735-739

MINERAL SURFACES AS A CRADLE OF PRIMORDIAL GENETIC MATERIAL

Enzo Gallori
Department of Animal Biology and Genetics, University of Florence, Florence, Italy.
gallori@dbag.unifi.it

ABSTRACT
Molecules which store genetic information (DNA and RNA) are central to all life on Earth. The formation of these complex molecules, and ultimately life, required specific conditions, including the synthesis and concentration of precursors (nucleotides), the joining of these monomers into larger molecules (polynucleotides), their protection in critical conditions (like those probably existing in primeval habitats), and the expression of the biological potential of the informational molecules (their capacity to multiply and evolve). Determining how these steps occurred and how the earliest genetic molecules originated on Earth is a problem that is far from being resolved.
Classical research in this field has focused on processes in aqueous solution; however it is difficult to conceive that complex molecules can be obtained by random collisions in a fully aqueous environment.
We believe that mineral surfaces, e.g. clay minerals, could have played a crucial role in the prebiotic formation of the biomolecules basic to life.
In this communication, I will discuss recent data from different fields strengthening the hypothesis, originally suggested by J.D. Bernal in 1951, of a surface-mediated origin of life.

THE LIPID WORLD: FROM CATALYTIC AND INFORMATIONAL HEAD-GROUPS TO MICELLE REPLICATION AND EVOLUTION WITHOUT NUCLEIC ACIDS

Doron Lancet, Barak Shenhav, Arren Bar-Even and Ron Kafri,
Dept. Molecular Genetics and the Crown Human Genome Center,
The Weizmann Institute of Science, Rehovot 76100, Israel.

ABSTRACT
A widespread notion is that life arose from a single molecular replicator, probably a self-copying polynucleotide in an "RNA world". We have proposed an alternative "Lipid World" scenario as an early evolutionary step in the emergence of cellular life on Earth. This concept combines the potential chemical activities of lipids and other amphiphiles, with their capacity to undergo spontaneous self-organization into supramolecular structures such as micelles and bilayers. In quantitative, chemically-realistic computer simulations of our Graded Autocatalysis Replication Domain (GARD) model, we have shown that prebiotic molecular networks, potentially existing within assemblies of lipid-like molecules, manifest a behavior similar to self reproduction or self-replication. What is being propagated is an epigenetic "compositional genome", i.e. the tally of each of the molecular species included.

In our model, lipids-like amphiphiles may possess a very large variety of chemical structures, including head-groups that resemble amino-acids or nucleotides. Catalysis is proposed to be exerted by such diverse chemical moieties, enhancing amphiphile exchange rates as well the formation of more complex head-groups with similarity to peptides or oligonucleotides. In a more recent version of our model (Polymer GARD or P-GARD), a path is delineated for the gradual transfer of from purely compositional information-storage capacity to increased dependence on linear molecular sequences. Our studies analyze in detail the properties of the emergent mutually catalytic networks within GARD assemblies, and show points of similarity and difference compared to present day cellular networks. We show that within a specific range of physicochemical interaction parameters, homeostatically stable stationary states ("composomes") emerge, capable of evolution-like progression towards higher complexity. Intriguingly, GARD may also provide a natural pathway for enantiomer selection in early biological systems.

Because amphiphile assemblies may form readily and spontaneously under prebiotic conditions, the Lipid World scenario may represent an intermediate "mesobiotic" phase, bridging an a-biotic random collection of organic molecules with a biotic protocell that contains long biopolymers, as well as more intricate information storage, catalysis and replication.

References
1. Segre, D., Ben-Eli, D., Deamer, D., Lancet, D. The lipid world. Origins Life Evol Biosphere, 31:119-145 (2001).
2. Segre, D., Ben-Eli, D., and Lancet, D. Compositional genomes: prebiotic information transfer in mutually catalytic non-covalent assemblies. Proc. Natl. Acad. Sci (USA) 97 (8): 4112-4117 (2000).
3. Segre, D., Shenhav, B., Kafri, R., and Lancet, D. The molecular roots of compositional inheritance. J. Theoret. Biol.. 213:481-491 (2001).
4. Shenhav, B.; Segre, D.; and Lancet, D. Mesobiotic emergence: molecular assemblies that self-replicate without biopolymers. Adv. Complex Systems 6(1): 15-35 (2003).
5. Segre, D., Lancet, D. Composing Life ­ EMBO Reports, 1(3): 217-222 (2000).

HISTORY OF WATER ON MARS

Philippe L. Masson
Université Paris-Sud
Département des Sciences de la Terre
Laboratoire OrsayTerre (FRE CNRS 2566)
Bât. 509, F-91405 Orsay Cedex (France)
masson@geol.u-psud.fr

ABSTRACT
Besides Earth, Mars is the only planet with a record of resurfacing processes and environmental circumstances that indicate the past and possibly recent operation of hydrologic activity. However the present-day conditions on Mars are far apart of supporting liquid water on the surface. Although the large-scale morphology of the Martian channels and valleys show remarkable similarities with fluid-eroded features on Earth, there are major differences in their size, small-scale morphology, inner channel structure and source regions indicating that the erosion on Mars has its own characteristic genesis and evolution. The different landforms related to fluvial, glacial and periglacial activities, their relations with volcanism, and the chronology of water-related processes, are presented.
A warmer, wet Mars with a dense atmosphere at the time after the heavy bombardment is supposed to provide the conditions for valley formation by running water. However, recent images obtained by the MOC experiment onboard Mars Global Surveyor show relatively young small-scale alcove-like gullies combined with small channels and aprons in the walls of impact craters, thus indicating even recent groundwater seepage and probably short-term surface runoff under almost current climatic conditions.

CURRENT STATUS OF THE SEARCH FOR EXTRASOLAR PLANETS

Michel MAYOR ,
Geneva Observatory, Switzerland

ABSTRACT
More than hundred extrasolar planets, orbiting other solar-type stars have been discovered on the last few years. These detections are not a priori surprising for astronomers. However the orbital properties of these exoplanets are really unexpected (very short orbital period, large eccentricities and in a few cases "supermassive" planets). That observed diversity of planetary systems has forced a rediscussion of scenarios of planetary formation.

Some attention will also be given to the most recent and unbiased comparisons of chemical properties of stars ,with or without giant planets. It is also interesting to consider first results on the role of stellar multiplicity on properties of exoplanets.

The observation of a planetary transit in 1999 allows the direct measurement of the radius and mean density of an exoplanet: the direct proof that these objects are really gaseous giant planets like Saturn or Jupiter in our own Solar System. New complementary spectroscopic observations begin to reveal physical properties of the planet itself as its chemical composition and properties of its atmosphere.

More and more extrasolar planetary systems with two or three planets are discovered . A fraction of them are systems with planets on resonant orbits.

Apart from the discussion of the status of the research on exoplanets, I would present the most exciting future experiments in that field.

SPONTANEOUS GENERATION OF AMINO ACID STRUCTURES
IN THE INTERSTELLAR MEDIUM

Dr. Uwe Meierhenrich
Univ. Bremen
Leobener Str.
D- 28359 Bremen
phone: +49-421 218 3401

ABSTRACT
In order to understand availability and distribution of molecular building blocks of biological systems during defined phases of the Chemical Evolution we studied and simulated interstellar processes in the laboratory. In dense interstellar clouds dust particles accrete ice mantles. As seen in infrared (IR) observations, this ice layer consists mainly of water ice, but also of carbon and nitrogen containing molecules. We deposited a gas mixture consisting of H2O, CO2, CO, CH3OH and NH3 onto an aluminium surface at 12 K under high vacuum, 10-7 mbar. During deposition the molecules were subjected to ultraviolet radiation with main intensity at Lyman-a. After warm-up, the refractory material was extracted from the aluminium block, hydrolysed for 24 h at 110 °C with 6 M HCl, derivatized and finally analysed by enantioselective gas chromatography coupled to a mass spectrometer. We were able to identify 16 amino acids in the room temperature products of irradiation [1]. The results were confirmed by parallel experiments using 13C-labelled ices in order to exclude contamination. A first 'group' of the identified amino acids was suggested to serve as the precursors of peptides and proteins. A second 'group' namely the diamino carboxylic acids is assumed to contribute to the development of the first genetic material, the peptide nucleic acid PNA. Beside the two groups of amino acids, N-heterocyclic organic molecules were identified that resemble the molecular building block of biological cofactors. The obtained results support the assumption that the photochemical products could be preserved in interstellar objects, and in term be delivered to the Earth during the heavy bombardment which ended about 3.8 Gyr ago. The remaining organic molecules might have played an important role on the appearance of primitive life on Earth. The identification of amino acids in interstellar ice analogues is suggested to be linked with the prebiotic development of proteins, genetic material and biological cofactors on Earth.

[1] G.M. Muñoz Caro, U.J. Meierhenrich, W.A. Schutte, B. Barbier, A. Arcones Sergovia, H. Rosenbauer, W.H.-P. Thiemann, A. Brack, J.M. Greenberg: Amino acids from ultraviolet irradiation of interstellar ice analogues. Nature 416 (2002), 403-406.

RECENT ADVANCES AND SETBACKS IN SEARCHING FOR THE OLDEST LIFE ON
EARTH ­ A GEOLOGIST'S VIEWPOINT

Stephen Moorbath
Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK
stephen.moorbath@earth.ox.ac.uk

ABSTRACT
In recent technical and popular scientific literature it has become almost axiomatic to claim that life began on Earth at least 3.9 - 4.0 billion (Ga) years ago. The most intense debate on earliest life centres around early Precambrian (Archaean) rocks from West Greenland, whose exact age, field relationships to dated rocks, geological identification, mode of genesis, interpretation of trace element abundances as well as carbon-isotopic abundance ratios, are in major dispute. These topics will be briefly discussed in the talk, and it is concluded that the most strongly disputed rocks (on Akilia Island, West Greenland) contain no record of biological activity whatever. Indeed, recent work (1) demonstrates that the crucial carbon-bearing rocks on Akilia Island, identified by several workers (2,3) as chemical sediments closely related to banded iron-formation (BIF), are actually banded quartz-pyroxene rocks of mixed igneous and metasomatic parentage which have no intrinsic biological significance.
Elsewhere in West Greenland, within the 3.7­3.8 Ga Isua Greenstone Belt (IGB), 13C ­ depletion in graphite particles in a genuine BIF has been claimed as evidence for biological activity (2). However, it has been shown (4) that this particular BIF was infiltrated by metasomatic carbonate fluids, in which metamorphic (thermal) disproportionation to elemental carbon has occurred. A further occurrence of IGB metamorphosed sedimentary rocks is claimed (5) to contain biogenic 13C - depleted graphite, possibly derived from the detritus of planktonic organisms. This occurrence is still under debate, but the overall evidence is highly speculative and requires much stronger evidence.
Repeated claims (e.g. 6) for 3.7 - 3.8 Ga spherical microbes in a horizon of IGB chert are implausible. These spheres occur in rocks which are extremely strongly deformed by stretching, and no spherical shape could possibly have been preserved from time of deposition. The spheres are almost certainly recent biological contaminants residing on the rock's surface and in cracks (7). Thus it is essential that all analysed ancient sedimentary rocks must be completely decontaminated from younger organisms before being tested by any technique for genuinely ancient biological activity. This is just as important for terrestrial rocks as it is for planetary samples. Indications are that such decontamination was not adequately carried out in some, or all, of the rocks discussed here.
Brief mention will be made of ongoing debate concerning the biogenicity of putative bacterial or cyanobacterial microfossils from 3.47 Ga Apex cherts in western Australia, long thought to provide the oldest morphological evidence for life on Earth (8). These microstructures have recently been reinterpreted (9) as secondary artefacts formed from amorphous graphite within multiple generations of metalliferous hydrothermal vein chert and volcanic glass, thus offering no support for primary biological morphology. Just as in Greenland (see above), a more realistic geological identification of the occurrence has cast severe doubt on the biological interpretation of these Apex chert microstructures.
Despite much effort, albeit hampered by varied geological misidentifications, there still appears to be no undisputed geological evidence for when and where life started on Earth. At any rate, popular suggestions for creation, or survival, of life in supposedly (and implausibly) sheltered environments during the putative, massive Late Heavy Bombardment of the Earth at around 3.9 ­ 4.0 Ga need no longer hold credence. We know for sure from the evidence of surviving rocks that by 3.7 ­ 3.8 Ga geological processes at and near the surface of the Earth were rapidly becoming recognisably uniformitarian, perhaps allowing life to get started in a more leisurely and unmolested fashion on mineral surfaces in Darwinian "warm little ponds".

References
(1) Fedo, C.M. and Whitehouse, M.J. (2002). Metasomatic origin of quartz ­ pyroxene rock, Akilia, Greenland, and implication for Earth's earliest life. Science 296, 1448 ­ 1452.
(2) Mojzsis, S.J., Arrhenius, G., McKeegan, K.D., Harrison, T.M., Nutman, A.P. and Friend, C.R.L. 1986. Evidence for Life on Earth before 3,800 million years ago. Nature 384, 55 ­ 59.
(3) Nutman, A.P., Mojzsis, S.J. and Friend, C.R.L. 1997. Recognition of > 3850 Ma water-lain sediments in West Greenland and their significance for the early Archaean Earth. Geochim. et Cosmochim. Acta 61, 2475 ­ 2484.
(4) Van Zuilen, M.A., Lepland, A. and Arrhenius, G. 2002. Reassessing the evidence for the earliest traces of life. Nature 418, 627 ­ 630.
(5) Rosing, M.T. 1999. 13C ­ depleted carbon microparticles in > 3700 ­ Ma sea-floor sedimentary rocks from West Greenland. Science 283, 674 ­ 676.
(6) Pflug, H.D. 2001. Earliest organic evolution. Essay to the memory of Bartholomew Nagy. Precambrian Res. 106, 79-91.
(7) Appel, P.W.U., Moorbath, S. and Myers, J.S. 2003. Isuasphaera isua (Pflug) revisited. Precambrian Res. In press.
(8) Schopf, J.W. 1993. Microfossils of the Early Archean Apex Chert: New evidence of the antiquity of life. Science 260, 640 ­ 646.
(9) Brasier, M.D. et al. 2002. Questioning the evidence for Earth's oldest fossils. Nature 416, 76 ­ 81.

PLANETS WITH DETECTABLE LIFE

Tobias Owen
Institute for Astronomy
University of Hawaii
Honolulu, HI, USA

ABSTRACT
We now know that more than 100 planets exist around stars other than the sun. Yet it appears that only one of these planetary systems may contain a planet with detectable life. This means it could have an Earth-like planet in its habitable zone. This outcome is less disturbing than it may appear, however, given the observational difficulties for finding such systems. Using ourselves as an example, we can assess the probability that such a planet will have acquired the necessary water and biogenic elements for life to begin. We can then consider the strategies for determining whether or not life exists on that planet at the present time.

CURRENT STATUS & EXPECTED EXOBIOLOGICAL RETURN
OF THE CASSINI-HUYGENS MISSION

François RAULIN
LISA - UMR 7583, CNRS & Universités Paris 12 et Paris 7, 61 Avenue du Général de Gaulle, 94010 Créteil Cedex France

ABSTRACT
The NASA-ESA Cassini-Huygens mission was successfully launched in October 1997. The spacecraft includes a Saturn orbiter and a Titan atmospheric probe. It has then been on an interplanetary trajectory toward Saturn. The Cassini Spacecraft flied-by Jupiter on December 2000 and will reach the Saturn system in 2004. Cassini will then become a Saturn orbiter and will fly-by its satellites, including the largest one, Titan. At the end of 2004, it will release the Huygens probe which will penetrate Titan's atmosphere on January 14, 2003. In 2000 an anomalous behavior concerning the relay link between the probe and the orbiter was identified, due to Doppler effect. It was putting into great danger the data transfer of the probe, and thus the whole Huygens probe mission. A joint ESA-NASA task force, the Huygens Rocovery Task Force was established in January 2001. The HRTF work was successfully conducted and a solution was identified, based on changing the Cassini trajectory. The trajectory now includes three new Titan fly-bys allowing to have a probe delivery at higher altitude of the orbiter, drastically reducing the Doppler effect and the resulting problem of data transfer. The Huygens mission is now safe again, as is the rest of the mission.
One of the main objectives of the Cassini-Huygens mission is to explore Titan in great detail and to study in particular the many exobiological aspects of Titan, this strange and exotic world which presents so many analogies with our planet. The Cassini orbiter and the Huygens probe, in a complementary way, will systematically study the many chemical and physical aspects of the different parts of what can be called the « geofluid » of Titan. Many of the twelve instruments of the Cassini orbiter and most of the six instruments of the Huygens probe will provide much information of crucial importance for our knowledge of the complexity of Titan's organic chemistry.
Indeed, because of the presence of a dense atmosphere, mainly made of N2 with noticeable fraction of CH4, and of an environment very rich in organics, and of many couplings involved in the various parts of its geofluid, in spite of low temperatures and the absence of liquid water, Titan is a reference for studying prebiotic chemistry on a planetary scale. Many programs have recently been developed to study in detail Titan's chemistry, in direct connection with the Cassini-Huygens mission (and even post-Cassini exploration of Titan ! !). They include new observations, development of photochemical models, laboratory determination of IR and UV spectra of organics of interest for Titan's atmosphere, and experimental studies, such as laboratory simulation of Titan's gas and aerosol organic chemistry.
The paper will present the current status of the Cassini-Huygens mission and will review the exobiological aspects of Titan. It will also present some of the new data concerning Titan's organic chemistry that have been obtained through the several possible approaches and discuss the exobiological implication of the potential scientific return of the Cassini-Huygens mission.

References
Coll et al, (2003), Oxirane: An exotic oxygenated organic compound in Titan? Astrophys. J, in press.
Lebreton, J.P., European Space Agency (1997). Huygens : Science, Payload and mission, ESA SP- 1177.
Lorenz, R. (2000). Post-Cassini Exploration of Titan : Science rational and mission concepts, J. Brit. Planet. Soc. 53, 218-2344.

Lorenz, R. and Mitton J. (2002). Lifting Titan's Veil. Cambridge Univ. Press, Cambridge, UK.
Raulin F. and T. Owen (2003). Organic chemistry and exobiology on Titan, Space Science Review., in press.
Ramirez et al, (2002). Complex Refractive Index of Titan's Aerosol Analogues in the 200-900 nm domain, Icarus, 156(2), 515-530 (2002).

VIABLE HALOBACTERIA FROM PERMIAN SALT DEPOSITS - AND IN OUTER SPACE ?

Helga Stan-Lotter
Institute of Genetics and General Biology, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria

ABSTRACT
From rock salt of Permo-Triassic age in an Austrian salt mine we isolated viable halophilic archaebacteria in recent years. Chemotaxonomic and molecular characterization of several strains led to their recognition as novel species. Two of those were designated Halococcus salifodinae and Halococcus dombrowskii. Several other coccoid isolates from British and German salt sediments of similar geological age proved to be members of the species H. salifodinae, as judged from their molecular, chemical and physiological properties. These microorganisms have apparently survived in the salt sediments over extremely long periods of time. Halobacteria could therefore be suitable model organisms for exploring the possibility of long-term survival of microbes on other planets. This notion appears all the more plausible since extraterrestrial halite has been detected in meteorites and is assumed to be present in the subsurface ocean on Europa. Our efforts are directed at the identification of the microbial content of ancient rock salt and the development of procedures for the investigation of the halobacterial response to extreme environmental conditions. The exploration of Mars is a target of space missions in the 21st century; therefore, testing the survival of haloarchaea under conditions comparable to present-day Mars, using a simulation chamber, was begun. Preliminary results with Halococcus and Halobacterium species suggested at least tenfold higher survival rates when cells were kept in liquid brines than under dry conditions; staining of cells with the LIFE/DEAD kit, which discriminates between damaged and intact membranes, corroborated these results.

ANCIENT LIFE ON EARTH AND MARS

1Mark A. van Zuilen, 2Aivo Lepland, 3Gustaf Arrhenius 1Centre de Recherches Pétrographiques et Géochimiques, 15 Rue Notre Dame des Pauvres, BP-20, 54501 Vandoeuvre les Nancy, France(markvz@crpg.cnrs-nancy.fr),
2Geological Survey of Norway, Leiv Eirikssonsvei 39, 7491 Trondheim, Norway, (aivo.lepland@ngu.no)
3University of California, San Diego, La Jolla CA 92093-0236, USA (arrhenius@ucsd.edu)

ABSTRACT
The search for signatures of extinct life on the early Earth is made difficult if not impossible due to poor preservation of the rock record. The very few exposed formations that date back beyond 3.5 Ga ago, have all been subject to high or intermediate grade metamorphism. This would have transformed the shapes of any microfossils beyond recognition, turned organic matter into kerogen and ultimately crystalline graphite. The search for life in Early Archean rocks therefore depends entirely on chemical and isotopic indicators. It is widely assumed that carbon isotope signatures of carbonaceous matter can be used to distinguish a biologic origin. However, such interpretations about ancient traces of life can only be made within the context of specific geologic circumstances requiring (1) control on recent contamination in the rock sample (is the carbonaceous material indigenous or exotic), (2) reliable protolith interpretation and control of secondary, metasomatic processes, (3) understanding of alternative abiogenic mechanisms that produce carbonaceous matter, and (4) understanding of the carbon isotopic systematics related to such processes.

A detailed study is presented of graphite occurring in different rock types in the 3.8 Ga Isua Supracrustal Belt (ISB), southern West Greenland. It will be shown that most graphite in Isua rocks is formed epigenetically either by dehydration and cooling of metamorphic fluids during serpentinization of ultramafic rocks, or by thermal disproportionation of siderite in secondary carbonate veins. Thermodynamic constraints of these processes and associated carbon isotope systematics are discussed.

The absence of an unambiguous record of life during Earth's earliest history, may be supplemented by a record of life on Mars. In the first billion years after formation this planet may have had an ocean and an active geological setting. Traces of early Martian life have been claimed in Martian meteorite ALH84001. However, it will be shown that biosignatures found in this meteorite can easily be explained by processes accompanying the thermal disproportionation of Fe-carbonates that is observed in the Isua Supracrustal Belt.

These problems, encountered with the tracing of life in altered rocks (either meteorites from Mars or highly metamorphosed Archean rocks), therefore highlight the need for in-situ analysis, or sample return of potentially relatively unaltered Martian marine or lacustrine sedimentary deposits, protected against radiation induced oxidation in the subsurface domain.

FACTORS LEADING TO THE APPEARANCE AND SURVIVAL OF METAZOAN EQUIVALENTS ON HABITABLE PLANETS

Peter D. Ward,
Department of Biology,
The University of Washington,
Seattle, USA 98195.

ABSTRACT
There is much new evidence supporting the hypothesis that metazoan equivalents require a narrow range of environmental conditions maintained over long periods of time, and that these two factors result in there being a relatively low percentage of metazoan-bearing planets. Microbial life, on the other hand, is probably widespread in the Universe, as evidences by the presence of extremophiles in a wide range of terrestrial environments. The requirements of metazoan life may include the following. In addition to a planet residing in the Continuous Habitable Zone allowing the existence of liquid water on its surface, additional requirements might include a relatively metal-rich star, plate tectonics, and a large Jupiter-type planet in a stable orbit outboard of the habitable planet. In the case of the Earth, additional elements fostering a diverse assemblage of animals and higher plants have been the presence of a large moon, an ocean that is only partly planet-covering, a magnetic field, and a position in the galaxy ensuring an abundance of metal, but a low incidence of nearby supernovae and close stellar encounters that cause mass extinctions. It is clear that our own planet has undergone very few mass extinction episodes. Here I will examine possibilities of the origin of life not on new planets, but on planets that have undergone sterilization due to large body impact or high energy bombardment from nearby supernova or gamma ray bursts. While most models for the origin of life start with planets with early ­Earth conditions, there may be quite different pathways on planets that already have oxygen and abundant organic constituents from the newly deceased.

EARLY LIFE AND HYDROTHERMAL ENVIRONMENTS

Frances WESTALL,
Centre de Biophysique moléculiare
CNRS
Rue Charles Sadron
45071 Orléans cedex 2,
France

ABSTRACT
The oldest rocks to provide information about the environment of early life, together with clear evidence of life, come from the Early Archaean greenstone terrains of Barberton in W. South Africa and the Pilbara in NW Australia. Geological investigations of these terrains document a sedimentary environment dominated by volcanic and hydrothermal (hot spring) activity that occurred both underwater and on land. Microbial mats formed at the edges of the vents and even on the cupola crowning the vent exits. Mats that formed further away from vent openings were, nevertheless, influenced by their effusions. It, thus, appears that early life on Earth was, by definition, thermophilic.