whence From life?
"Earth 4.5 AE B.C. Fishing is extremely poor, especially in August."
Ge/Ay133
Cliff Hauptman, The Complete History of Fishing
What steps are necessary for life as we know it? Raw materials
Monomers
Polymers
Once polymers are formed: Isolate,
Amino acids. Enzymes, structural motifs (muscle, nerves, ribosomes...). Lipids. Triglycerides are widely used energy sources. Phospholipids are widely used in membranes. Carbohydrates. Energy storage, DNA/RNA component. In plants, cellulose & pectin are used to construct cell walls. Nucleic acids. DNA for information storage, RNA for protein synthesis (& the genetic medium for some viruses).
Geochemical partitioning is sensitive to the depth at which silicates last "see" Fe/Ni metal.
The atmosphere is also strongly affected by core formation, and its timing.
SiO2 + 2Fe3O4 3Fe2SiO4 + 02
Equilibrium Gas Abundances in Silicate Magmas
SiO2 + 2Fe + O2 Fe2SiO4
The atmosphere is also strongly affected by core formation, and its timing.
Can build monomers from simple precursors in a variety of ways, but you need reduced carbon as a raw stock. Not much present in early Earth atmosphere?
Complex nebular organics?
An amazing variety of organics are found in chondrite matrices, esp. a wide variety of aliphatic and aromatic hydrocarbons, carboxylic acids, amino acids, purines, pyrimidines, and sugars. Synthesis?
D values are large, structural diversity complete. Supposedly formed by aqueous alteration of ISM precursors on parent bodies, but organic and silicate aqueous signatures are contradictory. Can the organics be made in the disk? The oxygen fugacity is critical.
Equilibrium Gas Abundances in Silicate Magmas
SiO2 + 2Fe3O4 3Fe2SiO4 + 02 Quartz Fayalite Magnetite (QFM) SiO2 + 2Fe + O2 Fe2SiO4 Quartz Iron Fayalite (QFI)
Might the exogenous delivery of organics to the early Earth been important?
Even large impacts likely have associated dust delivery (K-T site):
AIB= amino iso-butyric acid, a non-terrestrial amino acid.
"Impact frustration"/ sterilization of life? Ishua sediments from 3.8 AE ago show carbon isotopic signatures consistent w/ life, or at least primitive biochemistry. How early did life, or at least the stages just prior to life, begin, and when?
500 km diameter impactor
Toward polymers: The "hydrolysis problem":
How, in the presence of liquid water, does the growth of polypeptides occur? Either the locale must provide a "drying" envrionment, or agents such as carbodiimides must be available that can update water as part of the reaction sequence. This is major a hurdle, because at each step the reactions with water are thermodynamically favored.
Energy? No photosynthesis... Must be chemically derived at first.
ATP is the major medium for the storage and exchange of chemical energy in all living organisms. Note that any of the four hydroxyl bearing C atoms in the ribose could be coupled chemically. What drove the selection for the 1' C?
Were polyphosphates available on the early Earth?
Chemical energy can be used to drive polymer formation, on the "right" surfaces such as clays.
Once invented, photosynthesis would confer a huge competitive advantage.
Environments for prebiotic synthesis? I. Shorelines? Good wet/dry for hydrolysis, but small area and impact sensitive. II. Hydrothermal vents?
Current vent systems
Lost City carbonate column
Environments for prebiotic synthesis? II. Vents (cont'd)
Distance (km)
+ Can make lots of species in situ, impact protected - Polymer formation zone is small, synthesis rates are small compared to the surface
Environments for prebiotic synthesis?
III. Bubbles?
+ Drying env., so you can make polymers, micelles. The surface area is huge. - Transitory. What would impacts do?
Inside versus outside, or How do I pass along what I have learned?
Coacervates (polymer colloids)
Protein microaggregates
Meteorite organics can self assemble!
Helps "jump start" the monomers polymers isolate reproduce
Geochem. Cosmochim. Acta 64, 329(2000)
L excess in Murray, Murchison meteorites (isovaline shown)? How might you generate such an excess? 14C - decay? S...