Transcript Stephan Hoyer

Stephan Hoyer
Physics 120 Seminar
21 April 2008
Answers:
1. Earth
2. ???
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Solvent
 Liquid water
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Energy source
 Photosynthesis – 98% of energy
 Chemolithotrophic – chemical redox reactions
 Heterotrophic – other organisms
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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
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Some sort of liquid is necessary
 Solid – no mixing
 Gas – too light
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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
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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 hot
Just right
(Mostly) too cold
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Run away positive feedback:
 Snowball Earth
 Greenhouse effect

Saved by negative feedback:
 Carbonate-silicate cycle
Hotter: faster weathering, more carbon gets trapped in the Earth
Negative feedback
Colder: slower weathering, more greenhouse gas
Relies on
volcanoes!
From Kasting, J.F. and Catling, D. Annu. Rev. Astrophys., 41, 429-463 (2003)
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?
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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
Microorganism
Physicochemical
parameter
Time of
exposure
Other information
Deinococcus
radiodurans
Ionizing radiation
5-20 hours
~20000 Gy
Streptococcus mitis
Surface of the moon
2.5 years
In a camera
Numerous
-20 °C
~106 years
Permafrost
Numerous
-193
>10 years
Liquid N2
Numerous
Aw < 0.75
>10 years
Vacuum
Halococcus salifodinae NaCl >30%
>106 years (?)
In salt crystals
Endospores (Bacillus,
Clostridium)
Heat, chemicals
>3000 years
Mummies, sediments
Endospores (Baccilus)
Outer space
6 years
Surface of a space
probe
Bacteria like structures on meteorite fragment
Source of life on Earth?
1996
These guys included powerpoints!