Transcript Ddddddd

ASTR/GEOL-2040: Search for life
in the Universe: Lecture 6
• Delivery of C and H2O
via comets & asteroids
• Seeding of life
Today
• Delivery of water & carbon by comets
• Panspermia (delivery of seeds for life)
• Reading:
– RGS pp. 23-34
– Lon pp. 383-384, 176, 112; 130-135
– BS pp. 121-127, 144-146
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Enough carbon in inner parts?
• [C]/[heavier]
• Normalized
Sun  1
• Earth: 30
Noticed in 1961 (J. Oro)
RGS p.22
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Puzzle
• Not much Carbon where liquid water
• A lot of carbon where water is frozen
What is the reason?
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Solar
nebula
• Wet:
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Radial T gradient
• From
1700 K
to 20 K
• Inner parts
fewer
volatile
compounds
• More
refractories
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How to define refractory?
Refractory = resistant
A.
B.
C.
D.
E.
Solidifies at high temperature
Melts at high temperature
High Boiling temperature
Evaporates at high temperature
Condenses at high temperature
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How to define refractory?
A.
B.
C.
D.
E.
Solidifies at high temperature
Melts at high temperature
High Boiling temperature
Evaporates at high temperature
Condenses at high temperature
Liquid phase does not always exist
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Phase diagram of water
• From
1700 K
to 20 K
• Refractory
minerals:
T50>1100K
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Earth: 1 atm = 1 hPa = 105 Pa, so its 1/1000
Table
• From
1700 K
to 20 K
• Refractory
minerals:
T50>1100K
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Carbon delivery (present rates)
• Which type is the greatest C source?
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Carbon delivery (present rates)
1.6
<0.001
2.6
• Which type is the greatest C source?
– Crater-forming bodies
– Arrive intermittently
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Carbon delivery (present rates)
1.6
<0.001
2.6
0.32
• Greatest organic C source?
• Compare with C of biomass: 6x1014 kg
– 6x1014 kg / 0.3x106 kg/yr = 20 x 108 yr = 2Gyr
Carbon delivery
• Somewhat more anorganic than organic C
– Organic C delivery continuous
• Enough to produce all C in biomass
– Early rates likely much higher; see moon
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Also water is volative
• Not much water during formation
– temperatures too high  dry accretion
• Possible solution:
– Late delivery from beyond ”snowline”
– Evidence: depletion wrt meteorites
• Low K/U (potassium to uranium ratio)
– Indicator of relative depletion of volatiles
15
Is wet accretion possible?
• Yes, by later inward migration
– Need to look at orbital dynamics
• Many body problem
– Can easily become unstable
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Nice
model
• Trial &
error
• Want
low
ecc’ty
of gas
giants
• Wet
Earth
Late heavy bombardment
• Nice model simulations
• Find animation???
Gomes et al. (2005, Nature 435, 466)
Late heavy bombardment
• Nice model simulations
• LHB theoretically possible
Gomes et al. (2005, Nature 435, 466)
Volatilized by impact?
• Wet: volatilized by impact
– If so: heavier isotopes enriched
• Earth: no (66Zn depleted wrt 64Zn)
– Moon: (66Zn enriched wrt 64Zn)
– So Earth never got volatiles in the first place
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Water on terrestrial planets
• Not much on Venus and Mars
– either acquired less than Earth,
– or lost more
• Earth: much is in the mantle (2-10 times)
– Venus: unclear (losses by impact & sol wind)
– Mars: loss by solar wind (MAVEN)
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Alternative: late delivery
• Also known as: late veneer
– comets & asteroids
– Formed beyond snow line
• Potential problem D/H ~ 3x10-4
– Ocean water D/H = 1.56x10-4
• But 103P/Hartley 2 (IR): comp. w/ Earth
• For the coma: core could be enriched
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Different types of comets
• From
From ... Col to last
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Panspermia
• Arrhenius (1859-1927): spores survived
• Lord Kelvin (1824-1907): via meteorites
• Allan Hills meteorite (ALH 84001)
–
–
–
–
–
4.5 Gyr: crystallized magma from Mars
4.0 Gyr: battered, but not ejected
3.6-1.8 Gyr: altered by water
1984: discovered in Antarctica
1996: NASA press conference
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Why not Panspermia
Earth  Mars?
A. Because of Earth’s atmosphere
B. Because Earth is too massive
C. Because Earth is closer to the Sun
D. Because of either B or C
E. Because of both B and C
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Why not Panspermia
Earth  Mars?
A. Because of Earth’s atmosphere
B. Because Earth is too massive
C. Because Earth is closer to the Sun
D. Because of either B or C
E. Because of both B and C
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Panspermia
• Not a hypothesis for origin of life
– We could be related to Martian life (think)
– Other way unlikely (against Sun, heavier)
• Bacteria  suspended animation
– Virtually no metabolism (bact spores)
– Hardy to heat, desiccation, radiation, chem.
• Record so far 250 Myr (Lon 384)
– Isolated bubbles, lake bed Salado in NM
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How to tell apart?
• How would you be able to tell
whether we are Martians?
• Discussion
• This about special properties of
our life
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Radio(active) resistance
• Arrhenius (1859-1927): spores survived
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Radiation dose
•
•
•
•
•
1 Gy (=Gray): SI unit for absorbed radiation
1 Gy = 1 J/kg (=100 rad)
Biological effect (dep. nature of radiation)
1 Sv (Sieverts) = 1 Gy for el. mag. rad.
= 10 Gy for fast neutrons, 20 for a particles
Lon p. 386
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Bacterial names
• Deinococcus radiodurans
– (D. Radiodurans)
• Escherichia coli
– (E. coli)
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Position in classification scheme
bacteria
bacteria
deinococcus-thermus
proteobacteria
deinococcales
enterobacteriales
deinococcaaceae
enterobacteriaceae
deinococcus
escherichia
radiodurans
coli
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Radiation
dose
• Deinococcus radiodurans
• (D. Radiodurans)
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Tardigrade
• Get picture...
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Next week’s material
• Domains of life & extremophiles
– Bacteria in antarctica survived -50 C (-58 F)
– LUCA, the last common ancestor
• RNA world
– It can also act as catalyst
– No proteins necessary
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Preparation for quiz #1
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Next week Thursday
Check all lectures: def of life, order/disorder,
Away from equilibrium
Natural selection
Carbon & Water, polar molecules
Lipids and other building blocks
Genetic code, A-T, G-C
Biomarkers, meteorites, Miller/Urey, ...
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