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Lecture 1: Life: How common? What is it? How can we find it? • Takeaway messages: – – – – Microbial life probably widespread More advanced life not so certain No definite proof as yet Difficult to define what it means to be alive Life on originated very early on • 3.5-4.0 BYA • Impacts could have been frequent • Life may have originated more than once • Inevitable, given the right conditions? Right conditions are common • Basic for Life As We Know It: – Liquid Water – Concentrated supply of organic material – Appropriate energy source • Water fairly abundant; need to be properly placed relative to star • C, H, O, N, P, S all relatively abundant • Large fraction of stars in the Galaxy provide steady, long-lived source of energy Life can thrive in forbidding environments • Microbial life found in: – Hot springs, hydrothermal vents on ocean floor, in salty, alkaline, or acid solutions – Even in radioactive waste dumps! • Extremophiles tell us that life can thrive, maybe originate in places than we used to think impossible Yellowstone Hot Spring QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncomp resse d) de com press or are nee ded to s ee this picture. Complex organic molecules found all over the Galaxy • Radio astronomers (1950-today) have found > 100 molecules in interstellar space • Comets, meteorites even larger inventory – Include fundmental building blocks of life – Murchison & other meteorites: amino acids, nucleotides, sugars Molecular clouds QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Molecules with Two Atoms H2 hydrogen CSi carbon monosilicide CS carbon monosulfide NS nitrogen monosulfide HCl hydrogen chloride KCl potassium chloride AlF alum’m monofluoride SiN silicon mononitride SiS silicon monosulfide OHhydroxyl radical CN cyanide radical CO+SO+ CH CH+ CO carbon monoxide CP carbon monophosphide NO nitric oxide SO sulfur monoxide NaCl sodium chloride AlClaluminum monochloride PN phosphorus mononitride SiO silicon monoxide NH imidyl radical C2diatomic carbon HFhydrogen fluoride Molecules with Seven Atoms CH3C2H methylacetylene CH3NH2 methylamine HC4CN cyanobutadiyne CH3CHO acetaldehyde CH2CHCN acrylonitrile C6H Molecules with Nine Atoms CH3)2O dimethyl ether C2H5CN ethylcyanide C2H5OH ethanol CH3C4H methylbutadiyne Molecules with Nine Atoms (CH3)2CO acetone CH3C4N?cyanomethylbutadiyne NH2CH2COOH? aminoacetic acid Seeding of life from planet to planet • Martian meteorites found on Earth – Kicked off by impacts, captured by Earth • Study of meteorites + analysis shows primitive organisms could survive • Once started on one planet, life could spread to all hospitable environments in that planetary system QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Many, even most stars have planets (we think) • Natural result of star formation • Protoplanetary disks common around young stars, protostars • Debris disks seen around more mature stars • Astronomers (UCB, etc) have found many (200 +) planets already QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Lots of stars --> Lots of planets • 10,000,000,000 stars in Milky Way • 10,000,000,000 galaxies in known U. • 10--followed by 19 0’s = number of stars in the U. • Even if a tiny fraction have planets, that’s a LOT of planets Life commonplace in U. • Given right conditions, life inevitable , right conditions found everywhere, life can live in much more hostile environments than we thought,complex organic molecules easily formed, planets are abundant • So if we look, we’ll find it (eventually) New field: Astrobiology • What are the general conditions needed for life to appear? • How common is it (really)? • Where will we find it, and how? • What will it be like? • HOLY GRAIL: Find SOMETHING biogenic and NOT from Earth What does “alive” mean? • Tough question. So far has eluded the best of them. • Is it like pornography: Can’t define it, but you know it when you see it? – Doesn’t that beg the question?? • Self-replicating? Not enough. • Most will agree: to be alive a system must EVOLVE to adapt to its environment. • Darwinian evolution --> Self-replication, selection, mutation How about digital life? • The Ancestor: 80 byte machine code • Self-replicating • Ancestor-->Daughters-->etc = making copies of the genetic code • Random mutations (1-->0 or 0-->1) • Fitness criteria-->compete for memory space • Q: Is it alive?? QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Tierra home page: http://www.his.atr.jp/~ray/tierra/index.html Don’t ask what it IS, but what it DOES? • Life METABOLIZES: interacts with and changes its immediate (maybe even global) environment • Certain substances taken in (through membrane), energy extracted, other chemicals exhausted • Changes to environment can be small and local up to massive and global Some changes due to metabolism • • • • Composition of the atmosphere Alters isotopic ratios Changes balance of enantiometers Affects relative abundances of organic molecules • Even extinct organisms leave trail: chemical, mineralogical, morphological QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Familiar example: O2 we breathe • Earth’s atmosphere is way out of chemical equilibrium • All the molecular Oxygen should go away (oxidizes) in ~ 4 Myrs • What’s the source of replenishment? LIFE, primarily MICROBES • Alien scientist looking at Earth would immediately suspect planet might be inhabited Solar system vs extra-solar searches • Quite different – Solar system searches much more detailed, primarily local – Looking for life outside the SS much cruder-->look for global biomarkers • In both cases: “follow the water” • Both cases require big investment Evidence for water on Mars? QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTi me™ and a TIFF ( Uncompressed) decompressor are needed to see thi s pi ctur e. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Lecture 1: Life: How common? What is it? How can we find it? • Takeaway messages: – – – – Microbial life probably widespread More advanced life not so certain No definite proof as yet Difficult to define what it means to be alive