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Astronomy 3040 Astrobiology Spring_2016 Day-13
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Extreme Life - Extremophiles Thermophiles – heat lovers Hyperthermophiles Black smokers (350 ˚ C) Hot springs
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Extreme Life - Extremophiles Psychrophiles – cold lovers Antarctica ice pack (-20 ˚ C) Also very dry Radiation hardened
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Extreme Life - Extremophiles Endoliths – within rocks Up to several km below ground Endospores (resting) – found on moon Could these survive interplanetary journeys?
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Other sources of organics Chemical reactions near deep-sea vents Material from space – meteorites, comets Organics can form in space? Protoplanet & solar nebula When was chemical ==> biological transition? DNA is a complex molecule.
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Migration of Life to Earth We've seen some organisms survive in space. Could life arise on Venus or Mars first? Possibility of migration 20,000 meteorites cataloged ~36 come from Mars. 1. Large impacts. 2. Survival during transit. 3. Atmo. entry. ALH840 0
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Transit Endoliths could survive both blast and entry. Transit survival depends on time in space. Most rocks millions or billions of years A few ten years or less. Probably no interstellar meteorites (none known). Why migration? Does life form easily on early Earth? Does life form too easily on any planet?
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Implications of Transit Of the early solar system planets Mercury and Moon are probably not favorable. Early Venus and Mars might have been hospitable. Migration from Earth? Why migration?
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Evolution of Life Major events. Early microbes – anaerobic (primitive atmosphere). Chemoautotrophes – underwater probably Photosynthesis – multiple steps to arise ~3.5 Gyr ago (stromatolites) Oxygen crisis ~2.4 Gyr ago? Evolution of Eukarya – cell complexity Symbiosis? Mitochondria & Chloroplasts
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Cambrian Explosion Life started slowly (?) Multi-cell organisms ~1.2 Gyr ago Microbes had 2+ Gyr by themselves Animals – little change from 1.2 – 0.7 Gyr ago Then a huge diversification 30 body plans 40 Myr for all this to occur.
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Why Cambrian Explosion Oxygen level reached a critical value Survival of large, energy-intensive life forms Genetic diversity of eukaryotes Climate change – coming out of snowball No efficient predators May explain why no similar explosion since.
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Colonization of Land Oxygen level reached a critical value Ozone could form UV protective layer. Need to evolve a method to obtain oxygen and nutrients. Plants first ~475 Myr ago Probably evolved from alga. Specialization in larger plants (leaves, roots) Amphibians and insects within 75 Myr
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Carboniferous Period By 360 Myr ago – vast forests, insects Flooded land masses – so little decay These deposits formed coal.
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Rise of Oxygen Critical to animal life Molecular Oxygen – reactive gas. Disappears quickly if not replenished Early – oxidation reactions (rust, iron-oxides...) Now – use by animals Cyanobacteria
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Timing Fossil and rock studies 2-3 Gyrs – banded iron formations < 1% of present level Sulfur isotope studies ~2.35 Gyrs for oxygen. Cyanobacteria started ~2.7 Gyrs (350 Myr gap) Removal by non-biologicals – oxidation Slow build-up – no “explosion” 200 Myr ago – first charcoal
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Implications If Earth is typical – probably few planets with complex, oxygen using life (rqr ~4 Gyr to form) If Earth was delayed – complex life might be flourishing elsewhere.
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Impacts & Extinction
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Early dinosaurs – 245 Myr ago. Evolved and ruled for 180 Myr Small mammals 65 Myrs ago, mass extinction – Why? Also took out ~99% of all life; 75% of all species K-T boundary layer 1978 – Luis & Walter Alvarez Cretaceous-Tertiary boundary – high in iridium.
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More Evidence Besides Iridium 1. high metal abundances – Os, Au, Pl 2. “Shocked Quartz” grains (high Temp, Press) 3. Spherical rock “droplets” 4. Soot (global fires)
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Oh yeah, a Crater!
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Other Mass Extinctions About every 65-75 Myr (5 major events) Other than impact - “nuclear winter” effect
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Other Ideas Active volcanic activity – climate change UV increase – mutation rates Supernovae – cosmic rays GRBs – destroy ozone layer What have we learned? It could happen again.
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Tunguska – 1908 40m airburst SL9 – 1994 Jupiter
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Human Evolution How did we evolve?
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