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Published byJesse Lindsey Modified over 9 years ago
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Bio 1229: Is there life on other planets?
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Astrobiology “Biology of the Stars” Seeks to understand how to recognise life on other planets Not as easy as it might first appear! A.k.a. “Exobiology”
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The Miller-Urey experiment CH 4, NH 3, H 2 O, H 2 Electrical discharge 1953 Science 117: 528-529
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What is ‘alive’? (NZ Education system) Movement Respiration Sensitivity Growth Reproduction Excretion Nutrition
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What is ‘alive’? Schulze-Makuch & Irwin, 2006 Composed of bounded compartments in thermodynamic disequilibrium with the environment Transforms energy to maintain a low-entropy state Encoding and transmission of information for self-replication.
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Everywhere we look on Earth, we find life… Many of these habitats are not so different from the ‘extreme’ environments found elsewhere in the solar system. (Rock fissures 2.8 km deep, >60°C, 28 Ma old!)
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Molecules, molecules Macromolecules and polymers essential for life On Earth: Carbon Common among the chemical species detected in space
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Organic molecules as evidence of life?
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Silicon-based life? Silanes could have many of the properties of carbon macromolecules… Silicon is not common in space (so far)…
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Is there water out there?
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Water – is it necessary? “Life, as we know it, consists of chemical interactions that take place in the liquid state” Schulze-Makuch & Irwin
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Properties of a good solvent for life… Allows some molecular stability But… enables chemical bonds to break Dissolves many (but not all) solutes Dense enough to maintain molecules near each other Upper and lower limits to liquid state Funnels evolution… Buffers against environmental fluctuations
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Ammonia Solid denser than liquid No protection from UV Reacts with oxygen (metabolism would have to be anaerobic) Highly basic (pH ~11.6 for a 1.7% solution) Replace C=O with N=O Phosphate analogues? Analogues to hydrolysis etc. mean that ‘proteins’ could be formed
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Other solvents… Organic solvents Protect against UV Possible need for a non-polar biochemistry Silanes…
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What is ‘alive’? Schulze-Makuch & Irwin, 2007 Composed of bounded compartments in thermodynamic disequilibrium with the environment Transforms energy to maintain a low-entropy state Encoding and transmission of information for self-replication.
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Energy transformation on Earth… Photosynthesis via chlorophyll Or… Photosynthesis via Rhodopsin
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Energy transformation on Earth… Chemoautotrophs Hydrogen Sulfide CO 2 +O 2 +4H 2 S → CH 2 O+4S+3H 2 O 6CO 2 +H 2 O+3H 2 S → C 6 H 12 O 6 +3H 2 SO 4 Ammonia Iron (Fe 2+ )
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Energy transformation… elsewhere… Unusual electromagnetic wavelengths (e.g. UV, IR) Osmotic gradients Strong thermal gradients Electromagnetic fields
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What is ‘alive’? Schulze-Makuch & Irwin, 2007 Composed of bounded compartments in thermodynamic disequilibrium with the environment Transforms energy to maintain a low-entropy state Encoding and transmission of information for self-replication.
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Transmission of information On Earth: DNA-RNA-Protein (DNAoffspring) RNADNAmRNAProtein (RNAoffspring)
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Transmission of information RNA world RNA can store & transmit information also has enzyme-like activity PNA world Peptide nucleic acids Very robust (but not found naturally on earth) PAH world Polycyclic aromatic hydrocarbon world All carbon-based… a Silane-nucleic acid world?
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Where might there be life? Earth-like planets Single star Not too hot or cold Not too big Abundant water, carbon 329 Extrasolar planets currently known
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Venus Earth’s ‘Evil Twin’ Runaway greenhouse effect Surface temperatures ~400 °C Highly acidic
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Venus Dark streaks are from an ‘unknown UV- absorbent material’… a product of microbial activity?
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Venus Life in the Atmosphere? Large, stable clouds In chemical disequilibrium COS, H 2 S, O 2, lower than expected CO C, P, N present Non-spherical particles of comparable size to microbes At 50 km 27-77 °C (300-350 K) pH ~0; ~100 kPa High concentrations (100’s of ppm) in lower clouds
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Mars Water, O 2, CO 2 Past life? Similar to current Dry Valleys…
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Titan Orbits Saturn Liquid methane
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Europa Orbits Jupiter 100km layer of water, liquid below surface Thermal vents? Active (fractures in surface) Heat generated by tidal energy?
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Summary Could there be life outside of Earth? Would we recognise it? Would it be bipedal, English- speaking and with funny forehead ridges?
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