Stephan Hoyer Physics 120 Seminar 21 April 2008

Answers: 1. Earth 2. ???

 Solvent  Liquid water  Energy source  Photosynthesis – 98% of energy  Chemolithotrophic – chemical redox reactions  Heterotrophic – other organisms  Elements necessary for life:  98%: C, H, N, O, P, S  2%: Na, Cl, K, F, Ca, Mg, B, Al, Si, Cr, Mg, Cu, Zn, Se, Sr, Mo, Ag, Sn, I, Pb, Ni, Br, Va

 Some sort of liquid is necessary  Solid – no mixing  Gas – too light  Water is special  High heat capacity – stable temperatures  Expansion on freezing – keeps ice floating so it can eventually melt  High dielectric constant – keeps charged groups separate  Universal solvent – makes lots of reactions work

 Structure is good for building complex molecules  Four bonds attaching to each C atom  Chirality  Far more common in the interstellar medium  90 carbon containing molecules found  9 silicon based molecules  The Earth is mostly silicon, but there’s carbon based life

Urey-Miller experiment: recreating primitive conditions of Earth Recently (2002): Bernstein et al create amino acids in conditions like interstellar medium at 15K

Too hotJust right(Mostly) too cold

 Run away positive feedback:  Snowball Earth  Greenhouse effect  Saved by negative feedback:  Carbonate-silicate cycle

From Kasting, J.F. and Catling, D. Annu. Rev. Astrophys., 41, (2003) Hotter: faster weathering, more carbon gets trapped in the Earth Colder: slower weathering, more greenhouse gas Relies on volcanoes! Negative feedback

The “habitable” zone and the continuously habitable zone -> need to satisfy conditions for liquid water for sufficiently long time

Has a liquid water ocean under an ice crust Energy due to tidal forces from Jupiter Maybe there’s life down there?

 Bacteria!  Only form of life for billions of years  Most abundent and diverse form of life  They use all sorts of energy sources  Extremophiles!

Surviving is way easier than growing MicroorganismPhysicochemical parameter Time of exposure Other information Deinococcus radiodurans Ionizing radiation5-20 hours~20000 Gy Streptococcus mitisSurface of the moon2.5 yearsIn a camera Numerous-20 °C~10 6 yearsPermafrost Numerous-193>10 yearsLiquid N 2 NumerousA w < 0.75>10 yearsVacuum Halococcus salifodinaeNaCl >30%>10 6 years (?)In salt crystals Endospores (Bacillus, Clostridium) Heat, chemicals>3000 yearsMummies, sediments Endospores (Baccilus)Outer space6 yearsSurface of a space probe

Bacteria like structures on meteorite fragment Source of life on Earth? 1996

These guys included powerpoints!