Summary by Dr. Fazale ("Fuz") Rana and Dr. Hugh Ross
- General Information
- Abiotic/Prebiotic Chemistry
- Extraterrestrial Organics
- Self-Replicating Systems/Catalysis
- Minimum Genomes
- The meeting was held at UC San Diego the week of 7/12-7/16 (1999). This campus has a strong origin of life presence. Some of the workers in the field who are affiliated with UCSD are: Stanley Miller; Leslie Orgel; Gerald Joyce; Reza Ghadiri; Russell Doolittle; Jeffery Bada and Gustaf Arrhenius.
1) UCSD; 2) ISSOL; 3) NSCORT (NASA Specialized Center for Research and Training in Exobiology); 4) Salk Institute of Biological Studies; 5) Scripps Institute of Oceanography; 6) Scripps Research Institute.
- NASA had high visibility at this meeting. NASA was promoting: two NSCORT programs, Exobiology at UCSD, and the New York Center for Studies of Origins of Life; the NASA Astrobiology Institute; the NASA Planetary Biology Internship for graduate students; and the NSCORT undergraduate intern program.
- ~90 Talks and ~150 Posters in:
1) Abiotic/Prebiotic Chemistry/Chemical Evolution; 2) Extraterrestrial Organics; 3) Homochirality;
4) Paleogeochemistry; 5) Self-Replicating Systems; 6) Catalysis; 7) Minimum Genomes;
8) Astrobiology/Exobiology; and 9) Mars
- There were ~300 attendees from all over the world. There was a particularly large international contingent and a large number of attendees from NASA. The low attendance is surprising given the location (balmy San Diego) and the frequency of this meeting (only once every three years).
- In general, very few young, up and coming workers are currently becoming newly active in origins of life research. Most of the participants are age-old origins of life veterans and their graduate students. It seems as if the field is dying.
- The meeting was dominated by an air of pessimism and frustration.
- There was an overall lack of excitement. Many of the participants seemed as if they were simply going through the motions.
- The agreed upon consensus is that the most likely atmosphere for the early earth (CO2 + N2 + H2O) does not support abiotic synthesis of organics.
Atmospheric Prebiotic Synthesis, F. Raulin (i1.1)
- Reducing atmosphere studies may have implication for other systems (Titan).
Atmospheric Prebiotic Synthesis, F. Raulin (i1.1)
- Origin of life researchers are looking to volcanic exhalations or extraterrestrial sources for the origin/delivery of prebiotic compounds on earth.
- Today volcanic exhalations are H2O, CO2 and SO2. It was hoped that in the past volcanic exhalations were reducing (H2O, CO, CO2, N2, H2). Volcanic lightning is the source of energy to drive prebiotic molecule synthesis. However, chromium-oxygen barometry puts constraints on gaseous emissions of volcanoes in the primitive earth. According to these measurements, volatiles released from volcanoes were identical to those exhaled today as far back as 4 BYA. These results force origin of life researchers to look elsewhere for reducing gases and prebiotic molecule synthesis.
Production of Reactive Nitrogen in Explosive Volcanic Clouds, R. Navarro-Gonzalez et al. (cA1.2)
Cr Oxygen Barometry: Oxidation State of Mantle Derived Volatiles Through Time. J. Delano. (cA1.4)
- An anoxic environment is needed for life. This is a basic requirement. Ionizing radiation from 40K and 235Ur decay in the earth's crust and oceans (hydrosphere) has up to now been ignored as a source of production of molecular, ionic and free-radical oxygen species from the breakdown of water. Because of the ubiquitous presence and independence of radiometric decay on environmental factors the production of these species was homogeneous, uninterrupted and undisturbed throughout the ancient earth's history. The hydrosphere of primitive earth had an intrinsic oxidizing capacity. This paper created a furor with audience members unsuccessfully trying to come up with ways to get rid of the oxygen being produced.
Oxygen and Oxidizing Free-Radicals in the Hydrosphere of Early Earth. I. Draganic (cA1.3)
- It has been proposed that biotic methane production by methanogens may have contributed to the greenhouse effect early in earth's history compensating for the reduced solar luminosity. As this work progresses, it may have powerful design implications and provide one explanation for the early appearance of archea on the earth.
Methane in the Archean Atmosphere. J. Kasting (cA1.1)
An Ecosystem Model for Prediction of Methane Flux into the Archean Atmosphere. J. Siefert et al. (p1.46)
See: Science 284 pp. 2111-2113 (1999)
- For extraterrestrial delivery to work, there needs to be a source of sugars. Murchinson has no sugars (glyceraldehyde), but does contain sugar alcohols (glycerol). The sugar alcohols that are present are by and large C2 and C3 sugar alcohols. The data presented to demonstrate the presence of C4 and and C5 (ribitol) sugar alcohols in Murchinson via Mass Spectral analysis is not convincing. (The interpretation of the MS data is questionable.) There is still no evidence for the required C5 sugars. Also, these sugar alcohols were detected at very low levels in Murchinson.
Polyhydroxylated Compounds in Carbonaceous Meteorites, G. Cooper et al. (i1.2)
- Stability of sugars is a big problem for the origin of life at hydrothermal vents. Borate has been demonstrated to stabilize the breakdown of glucose via complex formation. However, as Robert Shapiro pointed out, the location of the borate ion in the borate-sugar stabilization complexes would preclude phosphorylation of the sugar.
TD-NMR Titration Studies on Complexation of Borate with Polyhydroxylated Organic Compounds. Implications for Chemical Evolution at High Temperature. V. Cimpoiasu et al. (p1.14)
Boron Compounds in the Primitive Earth. Implications for Prebiotic Evolution. R. Scorei et al. (c1.4)
- This was identified as a fundamental problem. Most of the focus is not on the regular backbone of purported replicator molecules in origin of life scenarios, but rather on the formation of the information-containing sequence of the R groups. All biomolecules (nucleic acids, proteins) and PNA (peptide nucleic acids) have regular backbones. It is assumed that there are no problems with regular backbones forming in the prebiotic world. However, the prebiotic soup is a complex mixture. Using molecule classes found in Murchinson it can be demonstrated that there are a number of reactions that will frustrate homopolymer formation. They include: 1) chain termination; 2) interruption; 3) reversal; 4) switching; 5) branching.
The Homopolymer Problem in the Origin of Life. R. Shapiro (cB2.8)
- It was demonstrated that rare earth metals, which would have been abundant in the primordial soup of the early earth, dephosphorylates nucleotides. This hydrolysis can be inhibited by proteins. However, gelatin, which is the most relevant model for prebiotic peptides in the primordial soup is not very effective at inhibiting the dephosphorylation reaction. The data presented indicated the need for huge amounts of protein (4 g/L) in the ocean to effectively inhibit this hydrolysis by the most effective inhibitor protein, albumin.
Dephosphorylating Activity of Rare Earth Elements and Its Implication in Chemical Evolution. M. Akaboshi et al. (p1.1)
- Phosphate, pyrophosphate and triphosphate substitution of nucleic acids promotes photolysis. Use of phosphite esters have been proposed as alternative systems for early genetic material. Data presented shows that phosphite esters are highly susceptible to hydrolysis. This work presents a significant obstacle to the formation of prebiotic nucleoside phosphate esters.
Phosphorus and the Origin of RNA World. W. Kongjiang (p1.32)
- With the recognition that the earth's early atmosphere cannot support abiotic synthesis of biomolecules and that volcanic exhalations in the early earth were not comprised of reducing gases, origin of life researchers are looking to interstellar dust in the proto-solar system for HCN and other pre-organics. In nearby circumstellar disks, pre-organics have been detected infalling into the protostar. These are faulty model systems for our solar system. Analysis of circumstellar disks at 4.5 billion light years away is needed to demonstrate this as the source of organics for our solar system. The presence of HCN is not sufficient in and of itself to produce organic molecules that can be converted to useful biological molecules. In the presence of water, HCN is quickly converted to formic acid via a formamide intermediate.
The Evolution of Early Earth Analogs, D. Koerner (i5.1)
- This still remains an unresolved problem after 45 years.
- At best, there is a minor chiral excess of [alpha]-methyl [alpha]-amino acids in Murchinson. However the data is not firm and may be an artifact of sample preparation procedure. There is no mechanism that explains the slight chiral excess.
Meteorite Amino Acids and the Origin of Homochirality. J. Cronin et al. (i2.2)
- Reflection Nebulae are identified as a possible source of circularly polarized light in the infrared. It is assumed that the circular polarization extends to the ultraviolet. Only 17% of observed light is circularly polarized in these systems. To induce chirality, there must be no other source of ultraviolet light, since nonpolarized ultraviolet radiation will indiscriminately destroy organics. If the circularly polarized light is too intense, it will increase the level of chiral excess, but also decrease the overall amount of organics. These offsetting factors will limit the chiral excess. Anything less than 100% chiral excess is useless for origin of life scenarios. Also, light must be monochromatic for chiral selective decomposition to take place. This condition is not met by any astronomical source.
Astronomical Sources of Circularized Polarization and the Origin of Homochirality. J. Bailey (c2.4)
See: Nature 389, p. 804 (1997)
- There were many proposed mechanisms for the origin of homochirality in the prebiotic world presented at the meeting. None of these mechanisms were compelling nor received broad-based enthusiasm or support.
See: (c2.5; c2.6; c2.7; p2.1; p2.4; p2.7; p2.9; p2.10).
- Particularly telling, was the question posed during the Homochirality Session, in which, a conference participant asked, "Why do we need homochirality for the origin of life?"
- 12C bias is due to kinetic effects in the carbon dioxide incorporation reactions of life. This marker is the most tenacious relic of early life. Photosynthesis is the most important pathway to establish the 12C enrichment. Currently, record for life on earth extends back to 3.8 BYA on earth. If 12C and 13C exchange occurs during metamorphosis, it will only result in the enrichment of 13C not in 12C. These results force us to accept the existence of life on earth prior to 3.8 BYA. This strongly suggests that the origin of life occurred rapidly.
Carbon Isotopes as a Biogeochemical Tool: Evolution of a Concept. M. Schidlowski (cB2.4)
- Values obtained from 12C enrichment data constrain the possible metabolic pathway. Reactive TCA: 5 - 20 (bacteria) ; 3-hydroxypropionate cycle: 10 - 15 (archae); Reductive Pentose Phosphate Cycle: 10 - 40 (bacteria); Reactive Acetyl CoA: 20 - 30 (archae).
Carbon Isotope Analyses of Individual Microscopic Fossils: A Novel Tool for Astrobiology. C. House, et al. (p5.8)
See: Science 283 pp. 674-676 (1999); Science 275 pp. 38-39 (1997); Nature 355 pp. 125-132 (1992); Nature 384 pp. 55-59 (1996); Nature 400 pp. 127-128 (1999).
- The degree of pre-planning, experimenter intervention and fine-tuning needed to get protein and nucleic acid self-replicating systems to work serves as powerful analogy for the need of a divine chemist. Furthermore, the systems currently available have parabolic kinetics in contrast to the exponential kinetics needed for Darwinian behavior.
Spread and More:Selection or Coesixtence of Parabolic Surface Replicators? G. von Kiedrowski (i3.1)
From Peptide Replicators to Self-Organized Networks. M Reza Ghadri (i3.3)
Towards The Selection of a Minimum Replicase. A. Azzawi et al. (p3.1)
- The current work on ribozyme evolution in the test tube to produce ribozymes with an increasingly broad range of catalytic activity is commonly regarded as providing support for the RNA world hypothesis. However, the need of enzymatic machinery, experimenter intervention and pre-planning indicate that this process would not be likely to work in nature.
Creation and Evolution of New Ribozymes. E. Schultes et al. (i3.2)
Towards in vitro Selectiion of Ribozymes with Polymerase Activity. K. Salehi-Ashtiani et al (c3.6)
in vitro Evolution of Ligase Ribozymes: Towards an RNA-Dependent RNA. K. McGinness et al (c3.7)
RNA-Catalyzed Pyrimidine Synthesis. P. Unaru et al. (cB3.1)
Selection of Catalytic RNA with Reduced Divalent Cation Dependence by Continuous Evolution in vitro. N. Lehman (cB3.2)
A Complex Ribozyme that Lacks Cytidine. J. Rogers et al. (cB3.4)
Also see: (p3.15; p3.16; p3.17)
- RNA production on catalytic surfaces (montmorillonite clay) does not happen spontaneously without the use of activated RNA nucleotides (a synthetic, non-naturally occurring product). Furthermore, both 2'-5' and 3'-5' linkages are formed. In the case of pyrimidines, most of the linkages are 2'-5'. This will not support the synthesis, selection and amplification of catalytic ribozymes needed to produce the required range of metabolic reactions to lead to life.
A Heterogeneous Self-Replicating RNA/Peptide Cycle. M. Levy et al. (P3.18)
Formation of RNA Oligomers by Montmorillonite Catalysis: A Model Study. G. Ertem et al. (p3.6)
Bridging the Prebiotic and RNA Worlds: Prebiotic Synthesis on Minerals. G. Ertem et al. (p3.7)
Hydrolysis of 3'5'- and 2'5' Linked Dinucleoside Monophosphate in Aqueous Solution at 175-240 °C. C. Kaede et al. (p3.11)
- With respect to error minimization, the possibility of evolving a genetic code as effective as the one found in nature is 1 in 106. This not an artifact of code history. The genetic code is not a `frozen accident'. This demonstrates a high degree of fine-tuning.
Has Natural Selection Shaped The Genetic Code? S. J. Freeland et al. (c4.5)
- Genomics has exposed problems with the current views regarding the evolutionary relationships of archea, bacteria and eucarya based on Carl Woese's 16s rRNA sequnce analysis. ~25% of all genomes are unique. From an evolutionary standpoint, there appears to be wide spread evidence for lateral gene transfer between the three kingdoms, gene deletion and gene duplication. Ribosomal protein sequences do not match the rRNA sequence data. Genes that are most frequently involved in lateral gene transfer support key metabolic processes, such as nitrogenase activity, etc. The likelihood of detecting horizontal gene transfers is inversely related to the ability to detect them. This makes organisms appear to be more closely related than they really are. It is currently questionable if evolutionary relationships can be established at the base of the phylogenetic tree. This entire field is in complete disarray as a result of the discoveries coming from full genome analysis.
Comparative Microbial Genetics: Insights on Physiology and Evolution. K. Nelson (i4.1)
Regrowing the Tree of Life. R. Doolittle (i4.3)
See: Science 284 pp. 1305-1307 (1999); Science 284 pp. 2124-2128 (1999); Nature 399 pp. 323-329 (1999).
- It is clear that the possibility of interplanetary transfer of life exists. Evidence presented suggests that interstellar transfer of life is highly unlikely. Radioactive decay will destroy life (235Ur and 40K). Dust particles are too small to protect internally located life. The stellar radiation needed to move dust particles is so intense as to guarentee the destruction of all prebiotics.
Survival and Biological Evolution of Life Beyond Its Planet of Origin. C. McKay et al. (i5.2)
- Based on geological evidence and modeling studies warm early Mars was dramatically transformed into cold arid Mars about 3.8 BYA. This occurred after a period of heavy bombardment in which sterilization impacts would have occurred. This work weakens the viability of Mars as a candidate for origin of life in the solar system.
The Habitability of Early Mars. M. Carr (i6.1)
- Volcanic exhalation on Mars as determined from Martian meteorites using chromium-oxygen barometery are similar in composition to those of earth as far back as 4 BYA. The non-reducing nature of the gases further weakens origin of life scenarios on Mars.
Cr Oxygen Barometry: Oxidation State of Mantle Derived Volatiles Through Time. J. Delano. (cA1.4)
- Evidence was presented (along the same lines as for ALH84001) for fossilized bacteria in the Nakhla Meteorite (1911 fall in the Nile Delta; dated at 1.3 B years old). There was concern expressed regarding the age of the meteorite and possibility of it being Martian-derived life in light of the results presented by Michael Carr. (Although the date of ALH84001 now serves to weaken a Martian origin of life, since Mars was not habitable 3.1 BYA).
Evidence for Mineralized Bacteria in the Martian Meteorite Nakhla. D. McKay et al. (c6.3)
- Data was present that demonstrated very powerfully the terrestrial contamination of the Nakhla meteorite via amino acid analysis of a sample taken from the meteorite's interior. This calls into question if the purported relics of life found in this meteorite are not from terrestrial contamination.
Amino Acids in Martian Meteorite Nakhla. D. Glavin et al (c6.4)
See: Proc. Natl. Acad. Sci. USA 96, pp. 8835-8838 (1999).