Transcript Ddddddd

ASTR/GEOL-2040: Search for life
in the Universe: Lecture 4
• Carbon in Universe
• Miller/Urey experiment
•Murchison meteorite
Question about O- last time
O-  negative ion
Example:
Phosphoric acid
H 3PO 4  3H   PO34-
 
ph   log H 
That’s why it’s nucleic acid!
nucleic because of nucleus
(but also prokaryotes have it)
 
if H   10
if H   10-7 then ph  7

-3
then ph  3
How they
polymerize
Takes care of one O-, but one remains
What we did last time
• Effects of mutations on DNA
– the cat ate the rat
• Biomarkers
– Fossil remains & atmospheric
– Often very subjective
• Life: far from equilibrium
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What is the energy source?
Example
Energy source Resulting activity
mountains
Atmosphere
El circuit
living cell
geothermal heat
Solar heating
Electric energy
Carbon supply
CO2+hn
or CH2O
Keeps rock rolling
Keeps rain coming
Keeps motor running
ADP  ATP
adenosine
triphosphate
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Commonalities:
• All life uses ATP
• All life uses same genetic code
 Common origin?
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Plan for today
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Organic matter in the Universe
Muchison meteorite
Miller/Urey experiment
Further reading:
– RGS pp. 13-17
– Lon pp. 370-375, 40-43
– BS pp. 233-238 (artificial life), 69-74
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Organic matter in the Universe
• Carbon comes from nuclear fusion in stars
• Late stages of evolution
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Life cycle of stars
• Carbon comes from nuclear fusion in stars
• Late stages of evolution
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Stellar evolution
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Stars consume food (H)
Expell waste (light, gas, dust)
Grow (protostar, main sequence, giant)
Die, and produce offspring from their dust
Are stars alive?
…discuss….
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Stellar “evolution”
• Not Darwinian evolution
• This ”life” cycle is more like a motor
• But let’s now look at their waste...
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Similarity of spectra with coal
• Circumstellar
envelope of
IRAS21282+5050
• Aromatic carbons
are common in
those parts of
space
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Molecules
around stars
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H2
CO, CO2
HCOOH
CH3-CH2-OH
NH3, HCN
H2S, N2O
C60, C70
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Protostellar/protoplanetary disk
• Interstellar medium:
T=30-100K
• Spinning disk
(angular momentum)
• Radius ~ 1000 AU
• Distance 150 pc
HL Tauri
Atacama Large Millimeter Array
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Protostellar/protoplanetary disk
• Forms rapidly
• This is a problem
• Disk becomes hot
(magnetic fields)
• Must cool rapidly
• 10 Myr: debris disk
• Inherits all organics
Disk fraction
Why short?
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How old are protostellar disks
A. As old as Earth?
B. 10 times younger?
C. 100 times younger?
D. 1000 times younger?
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Organics during planet formation
• Mix & produce disorder if left alone
 equilibrium
• Need to produce order
 drive away from equilibrium
• Need energy for this
Disk fraction
Why short?
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Energy sources on Earth
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Reducing atmosphere:
H2, H2O, NH3, CH4,
Discharges
Steam
Lightning a possible energy source
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Letter Darwin  Hooker (1871)
• ”... we could conceive in some warm
little pond, with all sorts of ammonia
and phosphoric salts, light, heat,
electricity, etc, present that a protein
compound was chemically formed
ready to undergo still more complex
changes”
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Comparison with
Frankenstein experiment
Low budget!
• Reducing
atmosphere:
• H2, H2O,
NH3, CH4,
Oparin/Haldane
• Discharges
• Steam
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Reducing? “Antioxidizing”
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Oxidizing Fe: 4Fe+3O2 2Fe2O3 (rust)
Oxidizing S: S+O2 SO2 (sulfurdioxide)
Reducing S: S+H2 H2S (hydrogen sulfide)
Reducing H2O: Fe+H2O  ’FeO’+H2
– Actually: 3Fe2SiO4+2H2O  2Fe3O4+SiO2+H2
– Fe2SiO4 (Fayalite), Fe3O4(magnetite)
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Problems with Miller/Urey?
• Now know: Methan & ammonia unlikely
– Experiment went out of fashion
– CO2 and N2 would have been abundant
• Miller forgot one of his vials: H2S
– Relevant to volcanos, recovered in 2007
– 23 amino acids!
• Main flaw: mass equilibrium: reactor design
Lon: p.215, BS: 207
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What we talked about
• Organic compounds can be made in space
• Meteorites can deliver amino acids and
some of the bases of DNA
• Also easily made in low-budget
Frankenstein experiment
• How to find in-depth reading material
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Next time
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Delivery of water & carbon by comets
Late heavy bombardment
Panspermia (delivery of seeds for life)
Reading:
– RGS pp. 23-34
– Lon pp. 383-384, 176, 112
– BS pp. 121-127, 144-146
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