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An Origin of Life in Salt Water or Fresh Water?
Returning to Darwin’s “Warm Little Pond”
-> The Terrestrial Origin of Life...
“Strong Inference, John Platt in Science-1964
“Strong inference consists of applying the following steps to
every problem ...
Charles Darwin’s Intuition-1871
"But if (and oh what a big if) we could conceive in
some warm little pond with all sorts o...
Working Model: Steps to an Origin of Cellular Life
1. There must be a non-enzymatic process by which potentially
functiona...
Platt’s Alternative Hypotheses and Crucial Experiment
Life must have begun in an aqueous medium which implies two
alternat...
I. Hydrothermal vents
Proposed by Corliss, Baross, Hoffman 1980s
Extended by Mike Russell and Bill Martin, 1990s
Laborator...
An origin of life at hydrothermal vents?
Vents would have existed on the early Earth
Chemical energy & some chemical inv...
II. Hydrothermal fields
Example: Bumpass Hell, Mount Lassen California
3 interfaces:
mineral/water
mineral/atmosphere
atmo...
Archaean hydrothermal field
“Hot Little Pool” Mt. Mutnovski, Kamchatka
4 amino acids
4 nucleobases (A,U,G,C)
Amphiphilic molecule
(14 carbon fatty aci...
Simulation chamber: many “hot little fluctuating pools”
CO2 atmosphere (anaerobic)
Elevated temperature 85 C
Acidic pH ran...
Gel elecrophoresis, nanopore sequencing, X-ray diffraction
Gel elecrophoresis
(Rajamani et al. 2008)
Evidence
-> RNA-like ...
When lipid vesicles are dried in the presence of solute molecules,
the solutes are captured between layers of a multilamel...
Lipid: decanoic acid+
decanoyl monoglyceride
Monomers: dAMP+TMP
Fluorescent stain: DAPI
When dried lamellae are exposed to...
Protocells cycle through three coupled phases
Polymers carried by stable protocells cycle between hydrated (top)
and dehyd...
Chemical Framework of the Terrestrial Origins of Life Model
The three coupled phases cycle polymers through the kinetic trap toward
increasing complexity through continuous synthesis...
These functions emerge as an evolutionary process that involves the following steps:
•An S-polymer arises by chance that s...
An Archaean volcanic landmass supports a hydrothermal field giving rise to
a sufficiently robust gel phase progenote (Woes...
Downhill distribution and
adaptive radiation…
…ultimately gives rise to LUCA
and marine stromatolites
Back to Darwin: from a “little warm pond” to the
“roots of the tree of life”?
The Terrestrial Origin of Life Model & Hypotheses
is offered to the community as a alternative
hypothesis and template for...
New work:
1.Archaean Simulation Chamber (McMaster University)
2.Fieldwork: Bumpass Hell (August 2016)
3.Combining species:...
Discussion:
Platt’s strong inference applied to an origin of life at
Hydrothermal Field vs. Hydrothermal Vent Sites
Using ...
Discussion: Limitations of Hydrothermal Vent Sites
- Vents lack an effective concentrating mechanism and energy
source to ...
Discussion: Limitations of Hydrothermal Vent Sites
- Salt and calcium ions (and additional divalent cations in the ancient...
Discussion: Limitations of Hydrothermal Vent Sites
Conclusions: these thermodynamic and kinetic barriers would be
present ...
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An Origin of Life in Salt Water or Fresh Water?

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Returning to Darwin's "Warm Little Pond" with the Terrestrial Origin of Life Hypothesis. Presented at the Australasian Astrobiology Meeting, Perth, July 2016. Presented by Dr. Bruce Damer, U.C. Santa Cruz.

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An Origin of Life in Salt Water or Fresh Water?

  1. 1. An Origin of Life in Salt Water or Fresh Water? Returning to Darwin’s “Warm Little Pond” -> The Terrestrial Origin of Life Hypothesis Australasian Astrobiology 2016, Curtin University Bruce Damer, University of California, Santa Cruz David Deamer, Martin Van Kranendonk, Malcolm Walter, Tara Djokic
  2. 2. “Strong Inference, John Platt in Science-1964 “Strong inference consists of applying the following steps to every problem in science, formally and explicitly and regularly 1.Devising alternative hypotheses 2.Devising a crucial experiment...with alternative possible outcomes, each of which will, as nearly as possible, exclude one or more of the hypotheses 3.Carrying out the experiment so as to get a clean result”
  3. 3. Charles Darwin’s Intuition-1871 "But if (and oh what a big if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts, light, heat, electricity etcetera present, that a protein compound was chemically formed, ready to undergo still more complex changes [..] " ~Charles Darwin, in a letter to Joseph Hooker (1871) “...some warm little pond“ or perhaps “...a hot, fluctuating little pool?”
  4. 4. Working Model: Steps to an Origin of Cellular Life 1. There must be a non-enzymatic process by which potentially functional, catalytic and replicating polymers of sufficient length are continuously synthesized and re-synthesized within a cycling system which drives Darwin’s “still more complex changes”. 2. The polymers must also be encapsulated by self-assembly within membranous compartments to prevent dispersion and allow selective transport, thereby forming vast numbers of protocells. 3. The protocells represent microscopic experiments in a natural version of combinatorial chemistry. A rare few happen to contain systems of polymers that stabilize their encapsulating protocell and catalyze their own reproduction. 4. These populations of functional systems are then selected by competition and interaction to be inherited by subsequent generations of protocells and evolve toward the first cellular life.
  5. 5. Platt’s Alternative Hypotheses and Crucial Experiment Life must have begun in an aqueous medium which implies two alternatives: salt water (99% of water on early Earth: hydrothermal vents or tidal pools) or fresh water (distilled water from precipitation: pools in hydrothermal fields found on volcanic landmasses) Chemical reactions require concentration and a source of energy -> eliminates dilute environments (open ocean, lakes, rivers). Alternative hypothesess: I. Hydrothermal vents (submarine-salt water) II. Hydrothermal fields (land surface-fresh water) Crucial experiment: 1. There must be a non-enzymatic process by which potentially functional, catalytic and replicating polymers of sufficient length are continuously synthesized and re-synthesized within a cycling system which drives Darwin’s “still more complex changes”.
  6. 6. I. Hydrothermal vents Proposed by Corliss, Baross, Hoffman 1980s Extended by Mike Russell and Bill Martin, 1990s Laboratory simulations by Herschey et al., 2014 and Burcar et al. 2015 Lost City - an alkaline hydrothermal vent
  7. 7. An origin of life at hydrothermal vents? Vents would have existed on the early Earth Chemical energy & some chemical inventory available Microbial life exists today in vent structures Q: How do hydrothermal vent environments satisfy the Crucial Experiment (synthesis and open ended complexification of systems of long chain polymers)? A: Thermondynamic barriers (hydrolysis) prevent the formation of biopolymers & salt water prevents the formation of stable membranous compartments (products are dispersed, no combinatorial selection). 30 years of laboratory work has so far failed to achieve this suggesting falsification of this approach.
  8. 8. II. Hydrothermal fields Example: Bumpass Hell, Mount Lassen California 3 interfaces: mineral/water mineral/atmosphere atmosphere/water. Only mineral/water in hydrothermal vents. Collection and concentration of large molecular inventory: extraterrestrial infall (lipid, amino acid, nucleobases, nutrients) + hydrothermal sources. Dilution in oceans. Access to 3 energy sources: heat activation, dehydration and sunlight. Regular cycling to drive reactions. Clays 90 C, pH~3 Wet-dry cycles
  9. 9. Archaean hydrothermal field
  10. 10. “Hot Little Pool” Mt. Mutnovski, Kamchatka 4 amino acids 4 nucleobases (A,U,G,C) Amphiphilic molecule (14 carbon fatty acid) Glycerol Phosphate pH 3 (mildly acidic) Testing the hypothesis in the field Membraneous structures form. Polymerization of RNA-like polymers has also been observed in exposure to hydrothermal field conditions.
  11. 11. Simulation chamber: many “hot little fluctuating pools” CO2 atmosphere (anaerobic) Elevated temperature 85 C Acidic pH range (pH 3) Testing the hypothesis in the lab -> RNA-like polymers are produced through a few cycles of 4-24 hours. Evidence will be presented next. Hydration-dehydration cycles with a range of reageants: AMP, UMP, lipid, etc. H2O rehydrationCO2 dehydration
  12. 12. Gel elecrophoresis, nanopore sequencing, X-ray diffraction Gel elecrophoresis (Rajamani et al. 2008) Evidence -> RNA-like polymers of AMP and UMP are produced in the 50-100mer range Nanopore sequencing (De Guzman et al. 2014) Polymer in presence of different lipids Polymer product through cycles -> Using hydration-dehydration other groups are polymerizing amino acids producing peptides (Hud et al., Cronin et al.). X-ray diffraction reveals AMP order in bilayer (Toppozini et al. 2013)
  13. 13. When lipid vesicles are dried in the presence of solute molecules, the solutes are captured between layers of a multilamellar matrix, ordered and polymerized through condensation reactions as water leaves. How it works – synthesis of polymers o o o o o o o o o o o o o o o oooo oo oo o o ooooo DRY FUSE MULTILAMELLAR LIPID MATRIX 2 µm 20 nm Phospholipid vesicles in water Dry multilamellar lipid phase
  14. 14. Lipid: decanoic acid+ decanoyl monoglyceride Monomers: dAMP+TMP Fluorescent stain: DAPI When dried lamellae are exposed to rehydration, large numbers of vesicles “bud off” some containing random polymers. Each provides a natural experiment in a natural combinatorial selection process. How it works – encapsulations of polymers We will now introduce the more speculative aspects of our work to satisfy steps 2-4 of the Working Model.
  15. 15. Protocells cycle through three coupled phases Polymers carried by stable protocells cycle between hydrated (top) and dehydrated (bottom) phases. If the rate of synthesis exceeds the rate of hydrolysis a kinetic trap is created permitting continuous re- synthesis and combinatorial selection of functional polymers. A growing population of stable protocells causes a third “gel phase” (center) to form. Micrographs shown to right.
  16. 16. Chemical Framework of the Terrestrial Origins of Life Model
  17. 17. The three coupled phases cycle polymers through the kinetic trap toward increasing complexity through continuous synthesis (dry), selection (wet) and interaction (gel). Competition and cooperation drive molecular evolution to gradually replace self-assembly processes with the functions of biology.
  18. 18. These functions emerge as an evolutionary process that involves the following steps: •An S-polymer arises by chance that stabilizes protocell membranes allowing them to survive to return their contents for re-synthesis in the anhydrous phase. • Protocells acquire P-polymers which enables access to nutrients through pores. • Metabolism generates products that support replication and systems of R- polymers that catalyze their own replication. Feedback through F- polymers provides controls for the rates of the above processes. • Access to nutrients supports metabolism through catalyzed M-polymers. Predictions on the Stepwise Emergence of Protocell Functions • Templating and coding through I-polymers provides inheritance of functional expression through cycles and initiates Darwinian selection.
  19. 19. An Archaean volcanic landmass supports a hydrothermal field giving rise to a sufficiently robust gel phase progenote (Woese, Fox 1977). Progenote distribution to additional aqueous environments permits adaptation to a gradient of conditions leading to the more challenging marine shorelines. Geological Framework of the Terrestrial Origins of Life Model
  20. 20. Downhill distribution and adaptive radiation… …ultimately gives rise to LUCA and marine stromatolites
  21. 21. Back to Darwin: from a “little warm pond” to the “roots of the tree of life”?
  22. 22. The Terrestrial Origin of Life Model & Hypotheses is offered to the community as a alternative hypothesis and template for experimentation. The full hypothesis is in publication as of May 2016 (Life) Commentary, teams and publications, testable hypotheses, experimental designs, and related work are being prepared at the Terrestrial Origins Wiki at: Origins.Biota.org Collaborators and Supporters UC Santa Cruz Australian Centre for Astrobiology McMaster University Center for Chemical Evolution, Georgia Tech Cronin Lab, University of Glasgow Resources and Acknowledgements University of Paris Harry Lonsdale Research Award NASA DigitalSpace Research Contact: Bruce Damer bdamer@ucsc.edu
  23. 23. New work: 1.Archaean Simulation Chamber (McMaster University) 2.Fieldwork: Bumpass Hell (August 2016) 3.Combining species: oligonucleotides & peptides 4.Conceptual work on the first genetic function: oligomers of an informational polymer & the “genetic cloud” 5.Definition of “rickety early life” and the candidate progenote. 6.Communal unit beginnings & extending evolutionary theory (Odling-Smee/Laland). 7.Scientific American article (Martin et al.)
  24. 24. Discussion: Platt’s strong inference applied to an origin of life at Hydrothermal Field vs. Hydrothermal Vent Sites Using analog laboratory and field experiments of hydrothermal field conditions we are capturing the physical energy of evaporation and concentration with the consequent reduction of water activity and changing it into the chemical energy of ester bond synthesis. We and our colleagues have demonstrated continuous non-enzymatic synthesis and re-synthesis of oligonucleotides and oligopeptides in lengths necessary to support the emergence of functions in a stepwise evolution of populations of protocells toward a form of pre-life capable of growth and adaptation In other words, the terrestrial, fresh water hydrothermal field hypothesis has satisfied our application of Platt’s crucial experiment.
  25. 25. Discussion: Limitations of Hydrothermal Vent Sites - Vents lack an effective concentrating mechanism and energy source to form sufficiently long polymers through diester bonds in nucleic acids and peptide bonds in proteins. In addition, polymers degrade through hydrolysis in the continuous presence of water so no kinetic trap mechanism can operate at these sites meaning that systems of polymers cannot move away from equilibrium. Condensation reaction to form ester bond, water must be a leaving group Consequence: there is a thermodynamic barrier against the formation of necessary polymers in the vent setting.
  26. 26. Discussion: Limitations of Hydrothermal Vent Sites - Salt and calcium ions (and additional divalent cations in the ancient oceans) inhibit assembly of membrane-bounded compartments. Life today has evolved complex homeostatic mechanisms to regulate cell volume by actively pumping osmotically active ions and thereby maintain transmembrane sodium and potassium gradients. This suggests that life adapted to marine environments later in its evolution (Mulkidjanian et al. 2012, Deamer and Georgiou 2015). - Mineral compartments may provide temporary localized concentration but are not selectively permeable or replicable and therefore cannot be a basis for combinatorial selection of large numbers of compartmentalized molecular systems. The necessary cycling through synthesis and testing required for polymers to undergo selection and molecular evolution is therefore not possible under these conditions. Any products of chemistry will be trapped indefinitely with the compartments or eventually lost to dispersion and degraded through hydrolysis. - Consequence: without effective compartmentalization there are dispersion and kinetic barriers to the evolution of systems of functional polymers.
  27. 27. Discussion: Limitations of Hydrothermal Vent Sites Conclusions: these thermodynamic and kinetic barriers would be present in hydrothermal vent environments on Enceladus (and Europa) as they are on the Earth. No vent analog experiment has demonstrated polymerization of sufficiently long polymers to exhibit function required by biology. No model for a kinetic trap supporting polymerization and repeated combinatorial selection of encapsulated systems of polymers has been observed at or proposed for a vent environment. In other words, the marine, salt water hydrothermal vent sites proposed as a hypothesis for an origin of life have yet to satisfy Platt’s crucial experiment and due to these barriers they may never be able to satisfy that requirement. Life as we know it, as it originated on Earth or could have originated on Mars could not have originated on Enceladus

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