Astronomy 3040 Astrobiology Spring_2016 Day-13

Extreme Life - Extremophiles Thermophiles – heat lovers Hyperthermophiles Black smokers (350 ˚ C) ‏ Hot springs

Extreme Life - Extremophiles Psychrophiles – cold lovers Antarctica ice pack (-20 ˚ C) ‏ Also very dry Radiation hardened

Extreme Life - Extremophiles Endoliths – within rocks Up to several km below ground Endospores (resting) – found on moon Could these survive interplanetary journeys?

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.

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

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?

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?

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

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.

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.

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

Carboniferous Period By 360 Myr ago – vast forests, insects Flooded land masses – so little decay These deposits formed coal.

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

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

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.

Impacts & Extinction

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.

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) ‏

Oh yeah, a Crater!

Other Mass Extinctions About every Myr (5 major events) ‏ Other than impact - “nuclear winter” effect

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.

Tunguska – m airburst SL9 – 1994 Jupiter

Human Evolution How did we evolve?