Science and Creationism 6. Abiogenesis © Colin Frayn,

© Colin Frayn, Abiogenesis Literally, the emergence of life from non-living origins This is organic chemistry, not biological evolution There are several competing ideas Bottom line: we really don’t know how this happened yet Yes, science has the guts to say “we don’t know”!

© Colin Frayn, Miller-Urey Stanley L. Miller & Harold C. Urey –1953, University of Chicago Experiment designed to simulate the early Earth Synthesised organic compounds –The building blocks of life First of many experiments –Using varying atmospheric assumptions –All 20 necessary amino acids can be synthesised easily

© Colin Frayn, Miller-Urey Apparatus

© Colin Frayn, Reducing Atmosphere (1) Miller & Urey assumed a ‘reducing’ atmosphere –Low in Oxygen, high in Hydrogen Some studies suggested this was not the case on the early Earth Latest studies favour reducing atmosphere –See e.g. Tian et al (2005), Schaefer & Fegley (2007) –Atmosphere was approximately 30-40% Hydrogen –Exactly as required Proofs: –Banded iron, Uraninite, paleosoils, pyrite

© Colin Frayn, Reducing Atmosphere (2) A reducing atmosphere is vulnerable to ultra-violet (UV) radiation –No oxygen to form ozone layer Ozone layer protects against UV radiation –Recent studies Effect of UV is less than was originally thought Aerosol haze can efficiently block UV radiation E.g. Zahnle (1986), Sagan & Chyba (1997) and Pavlov et al (2000) If life developed close to deep-sea hydrothermal vents then the UV was not a problem!

© Colin Frayn, Autocatalysis What came first, DNA or proteins? –DNA is needed as a pattern for proteins –Proteins are needed to catalyse DNA –Chicken and egg? RNA can auto-catalyse –RNA is very similar to DNA –We still have RNA in our body cells –It can catalyse its own reactions –RNA is a plausible precursor to DNA

© Colin Frayn, Hydrothermal Vents Discovered in 1949 First imaged in 1977 Unique ecosystems Under many kilometres of water

© Colin Frayn, How did RNA arise? RNA is (probably) too complex to have arisen in one step –Plausible precursors are required Benefits of RNA –Can replicate itself –Is simpler than DNA –Can self-catalyse –Cell replication apparatus is RNA Formation of RNA through ribonucleotides –Problematic as ribose is difficult to form –Maybe ribonucleotides arose through a different process? –Nature, 459, pp , Powner, Gerland & Sutherland (2009)

© Colin Frayn, From RNA to Cells Lipids spontaneously form bilayer ‘vesicles’ –These are spherical shells on a molecular scale –They can contain self-replicating RNA strands –This provides an ideal, self-contained environment Problems –How to form sufficient concentrations of lipids? –Work is on-going –E.g. Szostak & team (Harvard) –Hydrothermal vents?

© Colin Frayn, A Likely Model Amino acids are formed –See the Miller-Urey Experiment Lipid bilayers form –These are observed to form spontaneously Self-replicating RNA strings arise –This stage is uncertain, but plausible –RNA is able to catalyse its own replication RNA strings merge with bilayer shells –Lipid bilayers form ‘vesicles’ or shells First cells form –All the components are held together in one place –Facilitates chemical processes

© Colin Frayn, Progress Recent studies have made solid progress, but abiogenesis remains a very complicated topic We are very slowly filling in the remaining gaps in our knowledge Don’t expect this to be ‘solved’ any time soon ‘Unknown’ ≠ ‘unknowable’ Don’t give in to intellectual cowardice and say “we can never explain this”!