EOS 260 Part II Flashcards
OILRIG
oxidation is loss, reduction is gain
geochemical oxidation states
doesn’t work to think of electron gain/loss in terms of reservoirs, must think of oxidation state in terms of compounds in them
Oxidation states of H
Reference species- H2O
Reduced- H2
oxidation states of C
reference species- CO2
reduced- CH4, CO
oxidations states of S
reference species- SO2
Reduced- S8
Oxidized- SO4 (2-)
fugacity
pressure value needed at a given temperature to make the properties of a non-ideal gas satisfy the equation for an ideal gas
used to infer oxygen fugacity from stable minerals
mineral redox buffers (ex. hematite-magnetite), in equilibrium at given oxidation state
oxidation states of iron
Fe (2+)- Ferrous, reduced, ex. mineral- wustite, FeO, soluble in water; Fe (3+)- Ferric, oxidized iron, ex mineralogy- hematite, Fe2O3, insoluble in water
magnetite
Fe3O4- mixed valence
i.e. FeO•Fe2O3
In a reducing atmosphere
lots of CH4, CO (reduced molecules)
evidence for redox state
geological indicators: reduced/oxidized minerals
modern geochemical evidence
geological indicators of redox state
redbeds
banded iron formations
certain detrital minerals
minerals in palaeosols
modern geochemical evidence of redox state
sulphur isotopes
trace metal abundances ex. (Mo)
Cr isotopes
Redbeds
detrital sed. rocks (lots of sandstone), with ferric (oxidized) Fe, form through subaerial alteration- deposited in air with lots of O2 available
Redbeds occur
only after ~2.3Ga
BIFs
alternating layers of magnetite/hematite and chert, deposited in anoxic H2O column, sedimentary rock
BIF sedimentation
ferrous Fe released at MOR– dissolved, transported in anoxic ocean– ferric precipitates where oxidation occurs; form major iron ores
indicator of oxygen
redbeds
anoxic oxidation
4Fe(2+) + CO2 + 11H2O +hv —- 4Fe(OH)3 + CH2O + 8H+
reducing power transferred from Fe(2+) to CH2O
BIF occurrences
frequency vs. years ago
1.5-4bya, mostly Precambrian (Archean), some proterozoic
Hamersley BIF
2.69-2.44Ga
deposition- 5x10^11 mol Fe/yr
1.25x10^11 mol O2 equiv. /yr
globally may have been 6X this
detrital uraninite
Archean U ores commonly detrital, imply anoxic event- UO2 would have oxidized and dissolved
detrital
deposited by rivers
mass-independent fractionation of S isotopes
requires photolysis by UV, which requires lack of ozone layer, which means lack of O2
S weird behaviour
δ33S, δ34S, different behaviours, increased weird behaviour ~2.5Ga, large increase in Δ33S ~2.5Ga
Ga =
billion years
S escape pathways
S8, SO2– need to get both forms out of atmosphere
most important geochemical change in history
anoxic- oxic atmosphere
reducing- oxidizing
oxygen level vs. age (Ga)
up to 2.5Ga- oxygen ~1ppb, MIF constraints, ~2Ga significant increase in O2 levels
present oxygen atmosphere
21% O2
3.7x10^19 mol O2
moles in atmosphere
1.8x10^20 mol
reserving oxygenic photosynthesis
respiration:
H2O + CO2– CH2O + O2
how to get O2 into atmosphere
Bury organic carbon in rocks- net oxygen source
marine productivity
103PgC/yr
burial flux
0.1PgC/yr
~10^13 mol/yr
total BOC
~10^21 mol, 25X the O2 in the atmosphere
accounting for oxidation
oxidants: in sediments (0.5), excess Fe3+ in igneous rocks (2.5)
reductants: reduced C in crust (~1.5), missing reductant (~1.5)
where is the rest of the O2
hydrogen escape
Hydrogen escape
H light- escapes atmosphere– oxygen source (splitting water)
photolysis of H2O
2H2O + hv — 4H(to space) + O2
hydrogen escape from H2O rich atmosphere
excess H2O in upper atmos. + energy source– hydrodynamic escape
energy limited
loose ocean worth of H in few hundred million years
hydrodynamic escape
hydrogen literally flows out
energy source for hydrodynamic escape
EUV- extreme UV radiation
limits rate of escape
hydrogen escape from normal atmosphere
H2O cold trapped at tropopause, diffusion limited, CH4 major H-bearing species, rate is small
normal atmosphere, ‘diffusion limited’
- total hydrogen mixing ratio: fH_total = 2fH2O + 4fCH4 +… very small
- buoyancy of light atoms above homopause
hydrogen escape rate from normal atmosphere
~10^10 mol O2/ yr
The Great Oxidation
~2.4Ga, reducing-oxidizing atmosphere, ~1ppmv-1% O2, biggest chemical transition in Earth history, changes in glaciation
bad hypotheses
- GO followed oxygenic photosynthesis (2.7Ga)
- there has always been high O2 in atmosphere
great oxidation box model
atmos/ocean reservoir of O2, CH4 flux between organic carbon
also—> hydrogen escape = constant x CH4
also<— volcanic gases, reduced Fe from mantle
conceptual model of the environment, pre-GO
anoxic atmos./ocean, stromatolite reefs– oxygenic photosyn.– sinking organic matter (requires decay path)
anoxic decay path for organic matter
fermentation followed by methanogenesis (methane formation)
2CH2O — CH4 + CO2
processes
- Primary Productivity
2i. Aerobic respiration
2ii. Methanogenesis - Atmospheric chemistry- methane oxidation
Methane oxidation
Net rxn: 2O2 + CH4 — 2H2O + CO2
methane oxidation rate constant
depends on OH availability
OH availability
produced by footless of H2O by UV
mostly deep in troposphere
depend on UV penetration to troposphere
UV photons today
attenuated in stratosphere by O3
bistability in atmospheric oxygen
Balanced (O2 + 1/2CH4) source— fast methane oxidation
or— slow methane oxidation
fast methane oxidation
low oxygen– no ozone– UV to troposphere– OH abundant– fast methane oxidation– low O2
slow methane oxidation
high oxygen– ozone layer– UV blocked— not much OH— slow methane oxidation– high O2 (can accumulate)
bistability graph
oxygen vs. NPP (input)
low O2 level stability– form O3 layer– ‘flip up’ to high O2 stability
instability in middle
closed cycle
production of methane and oxygen — atmospheric chemical destruction
to support reducing atmosphere
need strong flux of reductants (Fe2+) to ‘tip the balance’ (of the closed cycle)
rate of hydrogen escape depends on
fH_total, depends on reductant input; more reducing atmos. = faster planetary oxidation
high oxygen stability
more stable state
once high oxygen is reached, unlikely it will be lost
GO biochemistry
metabolisms, NPP
GO atmospheric chemistry
methane oxidation
GO upper atmosphere physics
hydrogen escape
GO aqueous chemistry
iron solubility
GO sedimentary geology
evidence for oxidation states
FYSP
faint young sun paradox- contradiction between observations of H2O_l early in Earth’s history, and Sun’s output only 70% as intense
Ice cover on Earth since 3Ga
globally- small periods in proterozoic, most of cryogen
regional- mostly Devonian- Permian
before 3.0Ga- not enough records
S 4.5bya
0.7S
Quasi-linear increase through time
feature of main sequence of stellar evolution
Energy deficit
σT^4 = (1-α) S/4
ΔF_s = (1-0.3)(1368/4)(1-0.8) = 50W/m^2
but no record of it being cold.. had to be warmer than today?
neoarchean S =
0.8S_o
deficit in solar forcing balanced with
radiative forcing
CO2
CH4
other GHGs
CO2 radiative forcing vs. concentration
50W/m^2 would require 80,000ppm
paleosols
fossilized soil in contact w/ atmos., look at mineral assemblage to determine if they could have been present w/ different CO2 levels
palaeosols show
10-100pCO2 at 2.5Ga ?
Methane radiative forcing
100ppm of CH4 gives 8-15W/m^2, not enough forcing
CO2 + CH4 forcing
~40W/m^2– need another 10
the missing F
turn up N2– pressure broadening
green line in graphs = 2XN2_atm levels– CO2 has higher forcing
pressure broadening
more molecules = more pressure = more molecular movement (more collisions with radiation)
measuring pressure in past
paleobarometer
methods for measure pressure in past
fossilized rain drop imprints (tell density)
other proposals for ‘the other 10’
mixture of other GHGs- ammonia, OCS, clouds
clouds
high clouds have strongest greenhouse effect– more low clouds? – very unknown
when is the cryogenian
650-750Ma, neo-proterozoic (top of the proterozoic)
importance of Cryogenian
extensive, Snowball Earth glaciations (pole-pole)
lead into second oxidation event
evolution of animals around this time
2 glaciations in cryogenian
- Sturtian (longer)
2. Marinoan
pole-pole glaciation
large ice cap instability (past ~30º)
sturtian timing
onset: 710-720 Ma
termination: 655-655 Ma
duration: 58Myr
Marinoan timing
onset: 640-660Ma
termination: 630-640Ma
duration: 4-14Ma
dating glacial onset/termination
O isotopes- get ‘reset’
U-Pb- volcanic ash right below/above glacial sediment
sedimentary record of a glacier
glaciers erode and deposit
produce variety of sediments/structures
glacial environment
ice– out wash plain
below ice– glacial till
post-glacial environment
till plain– terminal moraine– pitted outwash plain
till
very poorly sorted sediment ranging in size from very fine grained to giant boulders
glacial deposits
till striated clasts glacial pavement dropstones polygonal sand wedges
glacial pavement
striations/grooves/chattermarks in bedrock
chattermark
something in bottom of glacier sticks for a bit then moves.. stick– move–stick–move
dropstone
glacier near body of water– iceberg– iceberg drops debris; warp layered beds; can cause folding (if high force)
glacial deposits
mostly around glacier margins
glacial movement
very dynamic, move all over the place all the time
polygonal sand wedges
freeze/thaw cycles at edge of glacier; ground water– ice– crack sed.– fill w/ sand– propagates; same shape as mud cracks, columnar joint
Importance of glacial deposit present locations
paleogeography, paleomagnetism– determining where continents were– determining if glaciation was low latitude
Paleomagnetism
rocks contain minerals w/ magnetic properties that align themselves w/ Earths dipole magnetic field; which way lines point- which way was up– determine paleo
flow/field lines
parallel to surface at equator
perpendicular to surface at pole
general cryogenian strat section, bottom up
coarse grain clastics– deep water carbonate– shallow water carbonate– fine grained clastic– glacigenic diamictice– DWC– SWC– glycogenic diamictice– DWC– SWC
in between glacial units (glacigenic diamictite)
we see carbonate– implies low latitude
diamictite
sedimentary rock that consists of a wide range of lithified, nonsorted to poorly sorted, terrigenous sediment, i.e. sand or larger size particles that are suspended in a mud matrix
Cryogenian BIFs
reappear in cryogenian after ~1Ga- dramatic drop in oxygen levels ~2-1bya- lower productivity
cap carbonates
unique facies found only after snowball earth glaciations; imply very rapid deposition post-snowball; deepening upward progression of facies (transgression)- CUS, finely laminated, mostly parallel
cap carbonate sequence
pre-glacial carb.– tillite– dolomite (dolostone, stromatolites, giant wave ripples, bariite)– limestone
piercing points
align split up formations- large basalt beds, large deformation belts
diamictite overlying carbonates
weird, till-cold, carbs-warm
commonly seen cap carb ‘package’
carb.–diamic–cap carb–carb platform– diamic–cap–carb–shale–till
carbonate platform
low latitude
fine sedimentfrom
slow rain out of ice shelf into underlying water
cap carb stromatolites
narrower, sharper than usual– indicate shallow water
types of low-latitude glaciation
hard snowball- thick (700m) over all oceans
open water- slushball, or Jormungand
Jormungand
thin belt of water around equator- ablation zone- old ice at tip of glacier- dirty, lower albedo
slushball
low-lat continental glaciation but sea-ice instability not reached
ice stability graph
stable state at ~10º, some open water
initiating a snowball
must lower CO2, reduce GHGs, decrease source, increase sink
decreasing GHG source
lower volcanism
increasing sinks
weathering, rock formation
silicate weathering feedback
negative feedback; temperature dependent; million year timescale
CO2 + CaSiO3— CaCO3 + SiO2
forward rxn: weathering
backward rxn: metamorphism
lichen evolution
increased weathering (acids), photosynthesis, change albedo; CO2 draw down, more nutrients to ocean– further CO2 drawdown
continents were at low latitudes
increasing albedo– increases Earth albedo (majority of insolation)– increases weathering
Franklin LIP
large basalt eruption, low latitude Large Igneous Province, easily weatherable- large CO2 sink, glaciation driver
continental area <15º latitude (%)
~25% at onset of glaciation (~5% 100Ma before that)
evidence of increased basalt weathering
Sr isotopes; decreases in 87Sr/86Sr before each of the glaciations
solar radiation absorbed
F_SW = (S/S_o)(S_o/4)(1-α)
Present day F_SW
239 W/m^2
deficit in solar radiation, and amount of CO2 needed to have a mean surface T equal to today, todays albedo
(0.94)(1368/4)(1-0.3) = 225W/m^2
∆F = 14W/m^2
~2-3000ppv CO2
deficit in solar radiation, and amount of CO2 needed to have a mean surface T equal to today, low lat. glaciation albedo = 0.6
F = 129 W/m^2
∆F = 110W/m^2
>1,000,000ppv CO2 (1bar) ?
300ppmv =
3x10^-4 ppv
300x10^-6 ppv
deglaciation requires
mean surface T 0ºC
∆T =
(alpha)(Forcing)
climate models require
0.1bar CO2 to exit snowball earth
cap carbonate problem
absence of primary carbonates during glaciation
fast deposition of thick cap carbonates following deglaciation
old thinking of cap carbonate
hard snowball– no air-sea gas exchange– volcanic CO2 accumulates in atmosphere– ice melts– CO2 invades ocean– flux of alkalinity from rapid weathering– cap carb deposition
enough CO2 to initiate warming and ice-albedo feedback
F = 90W/m^2
0.5bar CO2
very close to models for rudimentary calculations, see if you can get these answers
problem with old thinking of cap carbonate problem
most likely some air-sea gas exchange taking place
new thinking of cap carbonates
gas exchange allowed– atmos. ocean equilib– warming w/ deglaciation– CO2 flux from O-A– decrease DIC– speciate toward CO3(2-)– higher Ω– higher carbonate precipitation
why no carbonate deposition
lower sea level– no suitable depositional environment
to deposit more carbonate; DIC vs. CO3(2-)
have to move to higher CO3(2-) or lower DIC, generally diagonally down to the right
was the ocean acid or neutral during glaciation
2 competing hypotheses
Acid- CO2 influx w/ no Alk flux
Neutral- continued Alk flux
which hypothesis is right? (acid or neutral)
likely somewhat acidic
DIC vs. pCO2— higher pCO2, regardless of Alk we are in the higher portion of the graph
Nitrogen discovered by
Daniel Rutherford, 1772
nitrogen rich air
Noxious, Mephitic air
how N was discovered
box of air w/ candle, candle absorbs O2, mouse in box, dies
N cycles
biologic - fast, dominates in short periods of time
geologic - slow
N characteristics
5th most abundant element in the solar system;
2 stable isotopes: 14N 99.634%, 15N (0.366%); geochemically flexible, lots of redox states, lots of transformations
nitrogen oxidation states
oxidations state and species V, NO3(-) **abundant III, NO2(-) II, NO I, N2O 0, N2 ** -I, NH2OH -II, N2H4 -III, NH4 **
N species most important for ocean biology
NO3
N2 in the atmosphere
dominant gas, 78%
N as a nutrient
very important, key ingredient in amino acids; triple bond very strong, requires lots of energy, limiting nutrient
fixing
breaking triple bond and incorporating N into biomolecules, N2– NO
natural N fixers
lightening (minor)- 5 Tg/yr
bacteria (major, dominant)- 252 Tg/yr, ~equal btw ocean/land
anthropogenic N fixing
Haber-Bosch process
make NH3 for fertilizer and explosives
N is fixed by using
nitrogenase enzyme
metal cofactors
metal cofactors
Fe-Mo (most efficient)
Fe-Fe
Fe-V less efficient
N sources before Haber-Bosch
gauno
Haber-Bosch
Fritz Haber, 1909; industrialized by Carl Bosch; react N2 with H2 at high pressure– NH3; 140 Tg/yr; may have extended WWI; has pushed N cycle way out of equilibriumm
N fixing reaction
N2– PN
particulate nitrogen
ammonification
PN– NH3 or NH4(+)
nitrification
NH4(+) — NO3(-)
bacterially mediated
organisms prefer N in what form
NH4(+)- easiest to incorporate
NO3(-) is most abundant bioavailable
denitrification
NO3(-)—- N2 or N2O
bacteria using NO3 in electron transport chain
largest N flux out of the ocean
denitrification - 240 Tg/yr
out of balance with input
known planets orbiting stars
~2000
NASA, Kepler
watches one portion of sky constantly for dips in output radiation of stars (planet going in front of star)
beginning of Gaia hypothesis
mars exploration
disequilibrium in earths atmosphere
due to life
indicate life
persistence of unstable gases in atmosphere
ex. CH4 only last ~10yrs: ice cores show ~500,000yrs of CH4
early mars
features indicative of flowing water but no atmosphere; mars has no plate tectonics; dead planet
how to find life
check atmos. composition for equilibrium by using slits to spread light (spectroscopy)
what you will see on a planet with no atmosphere
theoretic Planck function
determining presence of atmosphere, start with
water; life as we know it is water dependent; less sunlight in, less IR out ≠ planck function, greenhouse effect
also look for
CO2, O2, O3, CH4
‘weird’ spectrums may equal life
a slice in time?
must look at whole earth history– Archean biosphere had very little O2 even with life
nitrogen cycle
Atm N2—dissolves ε=(-)0.6‰—N2—N fixing ε=0— PN—Ammonification ε=3‰— NH4—- Nitrification ε=+7‰ — NO3– Denitrification ε=25‰— N2— Atm N2
Denitrification ε
= 25‰
enriches light isotope use– heavy isotopes left behind
denitrification occurs
at boundary between oxic and anoxic layers
Tg
10^12
δ15N in plants on various substrates
N-rick substrate (schist): δ15N_plant = δ15N_rock
N-poor substrate (granite): δ15N_plant < δ15N_soil < δ15N_rock
plant growth vs. δ15N_plant
increasing δ15N = increasing growth; δ15N > 0 are all spawning sites– salmon bring in isotopically heavy N; δ15N_ocean > δ15N_land
anthropogenic climate change and N use on the N cycle
land-use change– atmospheric CO2, PP
FF burning– atmosph. CO2, N– climate warming– everything
Industrial N fixing- biologically available
large impacts, overall effects unknown- also increase weathering, release rock NH4
δ15N and age, vs. [N]
most values are δ15N = 0-10.. for all ages; ~2.4Ga very anomalous- δ15N values from 0-50
why was δ15N so high 2.4Ga
the great oxidation– beginning of nitrification; before 2.4Ga there was no nitrate in the ocean
N-fixation, δ15N vs TOC
δ15N = 0-(-2) –– Nitrogenase enzyme with Mo and Fe
δ15N = (-6) - (-8)––– nitogenase w/ V, or 2Fe
majority of values are in the 0-2 range.. modern style
why Fe, Mo enzyme is ‘modern style’
Vnf, Anf, are less efficient and = higher fractionation (more -)
Archaen nitrogenase enzyme
Fe-Fe, Fe was very soluble and abundant, Mo was insoluble due to anoxic waters
geological N cycles
sedimentation
hydrothermal alteration
N cycle, sedimentation
PN sink– deposited– nitrification/denitrification in sed.– converts to NH4+– substitutes into clay minerals
NH4+ substitution into clay mineral
similar ionic radius as K+ (1.61-1.69 vs. 1.46-1.63 Å), can substitute for K+, especially in K; average concentration = 430±25ppm
N cycle, hydrothermal alteration
new oceanic crust = low N (~1ppm)– hydrothermal alteration transfers N from O-rocks– increases concentration up to ~7ppm
ocean crust
basalt and gabbro
where to look for life
circumstellar habitable zone; not too cold, not too hot, just right
boundaries on habitable zone
runaway greenhouse– hydrogen escape– ø —snowball earth– CO2 condenses
early life, exploiting chemical gradients
chemolithoautotrophic– limited by gradients set up in natural environment
after great oxidation, life using existing gradients
heterotrophic
photoautotrophic
shift in life– huge earth change– gave life unlimited energy supply
evolution of human systems
hunter/gatherer––farming–– FF burning–– Nuclear––Solar
use of existing resource–– big resource change–– potential to have unlimited energy depending on our next steps; human system evolution somewhat parallels life system evolution
remarkable stable time in Earths history
Holocene, last 10,000yrs
unprecedented within last few million years
climate stability leads to
societal growth
climate sensitivity
~3ºC, changes through time
climate change scenarios
usually underestimate changes
<450ppm CO2
ice on Antarctica
> 450ppm CO2
no ice anywhere
last ppm we will likely see a Holocene like climate
350
how to deal with climate change
stop changing things or adapt
land surface that is crop land
12%
rivers that run dry before they reach the ocean, due to human extraction
25%
sources of nitrogen fixation
marine: ~100 ?g/yr
terrestrial: ~100 ?g/yr
industrial Haber-Bosch: ~100 ?g/yr
pre-industrial aragonite saturation
3.44
carbonate ion concentration
16%
effects of anthropogenic N use
eutrophication
biggest international transfer of fixed nitrogen
food (shipping crops)
Phosphorus use
extraction since pre-industrial has increased by a factor of 20
N subduction zones
hot subduction zone- more N volatilized
cold subduction zone- more N survives past subduction barrier
N that makes it past the subduction barrier
possibly sequestered into the mantle
calculating N in the mantle
noble gasses
xenoliths and diamonds
experimental petrology
N in atmosphere
4x10^18 kg N
calculating mantle N w/ noble gasses
Ar, N2 similar behaviour in basaltic melt: measure N2/Ar ratio in basalt- estime N content of mantle
MORB N2:Ar
~120
OIB N2:Ar
~9300
how to measure Ar/N2
calculate 40Ar in mantle, from?
proportion MORB, OIB source mantle: 80:120, use K concentration and decay rate, find total 40Ar in Earths history
OIB
ocean island basalt
BSE
bulk silicate earth
K concentration
280±120ppm
0.0117% 40K
40K decay
10.72%
total 40Ar in Earths history
4.2±1.8x10^18 mol
calculate N2 abundance
(4. 2±1.8x10^18mol - atmosphere 1.65x10^18mol - cont. crust 0.35x10^18) = 2.2±1.8x10^18mol
2. 2±1.8 x 120 and 9300 = N2 abundance
N2 abundance
24±16x10^18 kg N
calculating mantle N with xenoliths
find total N = 7x10^18kg in upper mantle; 3X smaller than N2/Ar estimate
N is more compatible
under reducing conditions- low oxygen activity, lots of eletrons
upper mantle minerals
olivine, pyroxene
upper mantle minerals sequester how much N
20 atmospheric masses, mostly in the lowermost upper mantle
TZ
transition zone: 410-660km depth
LM
lower mantle: ≤660km to core-mantle boundary
N in TZ and LM
TZ, LM reduced–– contain metallic Fe, N loves Fe, can dissolve NH4, or bond and make FeN nitrides; potential to hold 3X more than atmos.
N2, 40Ar correlation indicates
- mantle N recycled
- mantle N came from surface
- N movement through BSE directly influenced evolution of atmosphere
- possible solution to FYSP
solution to FYSP?
more N2 in atmosphere makes CO2 a more efficient GHG
core N
lots of Fe, N very soluble in Fe
estimate of amount: 180-300x10^18kg
core mass
1.83x10^24kg
cornerstone of climate science
Milankovitch hypothesis
variations in atmospheric CO2
lag change of global ice volume- insolation variations have a bigger impact than CO2 on ice volume
suggested Milankovitch hypothesis
orbitally-induced variations in summertime insolation in the norther high latitudes are in antipodes with the time rate of change of ice sheet volume
direct physical connection to insolation variations
rate of change of ice volume dV/dt
importance of ice sheet parameters
volume: matters most for sea level change; ice sheet extent: matters most for albedo; ice sheet hight: matters most for atmospheric circulation
A physical basis for life detection experiments
Lovelock, 1965; experiment in ET life should include- definition of life in terms favourable for recognition, description of past and present environment of planet to be sampled
physical basis of life
life is one member of the class of phenomena which are open or continuous reaction systems able to decrease their entropy at the expense of substances or energy taken in from the environment and subsequently rejected in a degraded form
broadness of physical basis of life
includes flames, vortex motion and others
wherever life exists, its biochemical form will be
strongly determined by the initiating event, environment at time of initiation
planet with life can be distinguished by
having orderliness, structures/events improbably in terms of thermodynamic equilibrium, extreme departures from an organic steady-state equilibrium of chemical potential
experiments for detection of life
search for order
search for non-equilibrium
search for order
gas chromatograph– mass speck seek ordered molecular sequences, chemical identities; seek ordered molecular weight distributions- biological polymers have sharply defined molecular weights (inorganics do not); listen for ordered sequences of sound
search for non-equilibrium
differential thermal analysis (DTA) to find chemical disequilibrium by comparing planet atmosphere with inert gas, likely to see a reaction if planet is in equilibrium; search for compounds that are incompatible in the long-term; apparatus to recognize objects in non-random motion
life ‘as we know it’ on mars?
-dry, -atmosphere thin, -no trace of O2, -less filtered insolation, -lots of UV, -possible large amount of nitrogen oxides
A search for life on Earth from the Galileo spacecraft
Sagan et al., 1993; look for indication of life on Earth; indications of life- abundant gaseous O2, atmospheric CH4 in disequilibrium, radio transmission (intelligence)
Implies oceans are composed of liquid water
high humidities over most of planet
why water is an ideal medium for life
dielectric constant, solvation properties, heat capacity, temperature range or liquid state
CH4 on Earth
CH4 oxidizes quickly, major discrepancy btw observation and thermodynamic equilibrium, ~1ppm, some mechanism is pumping CH4 into atmosphere, strong indication of life
N2O on Earth
atmospheric life = ~50yrs, non-biological mechanisms are too minuscule to contribute as much as is seen
unusual RED spectral imaging
corresponds to no plausible mineral- signature of light-harvesting pigment in a photosynthetic system (chlorophyll a,b)
radio waves
asymmetry- detected on night-side (can escape ionosphere), constant frequencies suggest artificial origin, pulse-like amplitude modulation- artificial, never observed for natural radio emissions
Bistability of atmospheric oxygen and the great oxidation
Goldblatt, 2006; history of earth = major transitions separated by long periods of relative stability
earths largest chemical transition
the Great Oxidation, ~2.4ba; [O2] rose from 0.01PAL
origin of oxygenic photosynthesis gave rise to
2 simultaneously stable steady states for atmospheric oxygen; low oxygen steady state persisted 300million years after onset of oxygenic photosyn.
Great Oxidation =
switch to high oxygen steady state
bistability from
UV shielding of troposphere by O3– nonlinear increase in lifetime of atmospheric O2
O2 before life
<10^-12 PAL
GO consequence of
oxygenic photsyn. occurred 300Myr prior; increased mantle outgassing, contradicts geological constraints; oxidation of crust- decreased metamorphic reductants ‘r’, increased primary productivity ‘N’
major metabolic pathway before GO
CO2 + H2O + hv––– 1/2CH4 + 1/2CO2 + O2
bistability feedback
O2 >2x10^-5PAL–– O3 forms–– decreased CH4 oxidation (reduced O2 sink)–– O2 levels increase–– further O3 formation
MIF
mass independent fractionation