EOS 260 Part II Flashcards
(277 cards)
1
Q
OILRIG
A
oxidation is loss, reduction is gain
2
Q
geochemical oxidation states
A
doesn’t work to think of electron gain/loss in terms of reservoirs, must think of oxidation state in terms of compounds in them
3
Q
Oxidation states of H
A
Reference species- H2O
Reduced- H2
4
Q
oxidation states of C
A
reference species- CO2
reduced- CH4, CO
5
Q
oxidations states of S
A
reference species- SO2
Reduced- S8
Oxidized- SO4 (2-)
6
Q
fugacity
A
pressure value needed at a given temperature to make the properties of a non-ideal gas satisfy the equation for an ideal gas
7
Q
used to infer oxygen fugacity from stable minerals
A
mineral redox buffers (ex. hematite-magnetite), in equilibrium at given oxidation state
8
Q
oxidation states of iron
A
Fe (2+)- Ferrous, reduced, ex. mineral- wustite, FeO, soluble in water; Fe (3+)- Ferric, oxidized iron, ex mineralogy- hematite, Fe2O3, insoluble in water
9
Q
magnetite
A
Fe3O4- mixed valence
i.e. FeO•Fe2O3
10
Q
In a reducing atmosphere
A
lots of CH4, CO (reduced molecules)
11
Q
evidence for redox state
A
geological indicators: reduced/oxidized minerals
modern geochemical evidence
12
Q
geological indicators of redox state
A
redbeds
banded iron formations
certain detrital minerals
minerals in palaeosols
13
Q
modern geochemical evidence of redox state
A
sulphur isotopes
trace metal abundances ex. (Mo)
Cr isotopes
14
Q
Redbeds
A
detrital sed. rocks (lots of sandstone), with ferric (oxidized) Fe, form through subaerial alteration- deposited in air with lots of O2 available
15
Q
Redbeds occur
A
only after ~2.3Ga
16
Q
BIFs
A
alternating layers of magnetite/hematite and chert, deposited in anoxic H2O column, sedimentary rock
17
Q
BIF sedimentation
A
ferrous Fe released at MOR– dissolved, transported in anoxic ocean– ferric precipitates where oxidation occurs; form major iron ores
18
Q
indicator of oxygen
A
redbeds
19
Q
anoxic oxidation
A
4Fe(2+) + CO2 + 11H2O +hv —- 4Fe(OH)3 + CH2O + 8H+
reducing power transferred from Fe(2+) to CH2O
20
Q
BIF occurrences
A
frequency vs. years ago
1.5-4bya, mostly Precambrian (Archean), some proterozoic
21
Q
Hamersley BIF
A
2.69-2.44Ga
deposition- 5x10^11 mol Fe/yr
1.25x10^11 mol O2 equiv. /yr
globally may have been 6X this
22
Q
detrital uraninite
A
Archean U ores commonly detrital, imply anoxic event- UO2 would have oxidized and dissolved
23
Q
detrital
A
deposited by rivers
24
Q
mass-independent fractionation of S isotopes
A
requires photolysis by UV, which requires lack of ozone layer, which means lack of O2
25
S weird behaviour
δ33S, δ34S, different behaviours, increased weird behaviour ~2.5Ga, large increase in Δ33S ~2.5Ga
26
Ga =
billion years
27
S escape pathways
S8, SO2-- need to get both forms out of atmosphere
28
most important geochemical change in history
anoxic- oxic atmosphere
| reducing- oxidizing
29
oxygen level vs. age (Ga)
up to 2.5Ga- oxygen ~1ppb, MIF constraints, ~2Ga significant increase in O2 levels
30
present oxygen atmosphere
21% O2
| 3.7x10^19 mol O2
31
moles in atmosphere
1.8x10^20 mol
32
reserving oxygenic photosynthesis
respiration:
| H2O + CO2-- CH2O + O2
33
how to get O2 into atmosphere
Bury organic carbon in rocks- net oxygen source
34
marine productivity
103PgC/yr
35
burial flux
0.1PgC/yr
| ~10^13 mol/yr
36
total BOC
~10^21 mol, 25X the O2 in the atmosphere
37
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)
38
where is the rest of the O2
hydrogen escape
39
Hydrogen escape
H light- escapes atmosphere-- oxygen source (splitting water)
40
photolysis of H2O
2H2O + hv --- 4H(to space) + O2
41
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
42
hydrodynamic escape
hydrogen literally flows out
43
energy source for hydrodynamic escape
EUV- extreme UV radiation
| limits rate of escape
44
hydrogen escape from normal atmosphere
H2O cold trapped at tropopause, diffusion limited, CH4 major H-bearing species, rate is small
45
normal atmosphere, 'diffusion limited'
- total hydrogen mixing ratio: fH_total = 2fH2O + 4fCH4 +... very small
- buoyancy of light atoms above homopause
46
hydrogen escape rate from normal atmosphere
~10^10 mol O2/ yr
47
The Great Oxidation
~2.4Ga, reducing-oxidizing atmosphere, ~1ppmv-1% O2, biggest chemical transition in Earth history, changes in glaciation
48
bad hypotheses
- GO followed oxygenic photosynthesis (2.7Ga)
| - there has always been high O2 in atmosphere
49
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
50
conceptual model of the environment, pre-GO
anoxic atmos./ocean, stromatolite reefs-- oxygenic photosyn.-- sinking organic matter (requires decay path)
51
anoxic decay path for organic matter
fermentation followed by methanogenesis (methane formation)
| 2CH2O --- CH4 + CO2
52
processes
1. Primary Productivity
2i. Aerobic respiration
2ii. Methanogenesis
3. Atmospheric chemistry- methane oxidation
53
Methane oxidation
Net rxn: 2O2 + CH4 --- 2H2O + CO2
54
methane oxidation rate constant
depends on OH availability
55
OH availability
produced by footless of H2O by UV
mostly deep in troposphere
depend on UV penetration to troposphere
56
UV photons today
attenuated in stratosphere by O3
57
bistability in atmospheric oxygen
Balanced (O2 + 1/2CH4) source--- fast methane oxidation
| or--- slow methane oxidation
58
fast methane oxidation
low oxygen-- no ozone-- UV to troposphere-- OH abundant-- fast methane oxidation-- low O2
59
slow methane oxidation
high oxygen-- ozone layer-- UV blocked--- not much OH--- slow methane oxidation-- high O2 (can accumulate)
60
bistability graph
oxygen vs. NPP (input)
low O2 level stability-- form O3 layer-- 'flip up' to high O2 stability
instability in middle
61
closed cycle
production of methane and oxygen --- atmospheric chemical destruction
62
to support reducing atmosphere
need strong flux of reductants (Fe2+) to 'tip the balance' (of the closed cycle)
63
rate of hydrogen escape depends on
fH_total, depends on reductant input; more reducing atmos. = faster planetary oxidation
64
high oxygen stability
more stable state
| once high oxygen is reached, unlikely it will be lost
65
GO biochemistry
metabolisms, NPP
66
GO atmospheric chemistry
methane oxidation
67
GO upper atmosphere physics
hydrogen escape
68
GO aqueous chemistry
iron solubility
69
GO sedimentary geology
evidence for oxidation states
70
FYSP
faint young sun paradox- contradiction between observations of H2O_l early in Earth's history, and Sun's output only 70% as intense
71
Ice cover on Earth since 3Ga
globally- small periods in proterozoic, most of cryogen
regional- mostly Devonian- Permian
before 3.0Ga- not enough records
72
S 4.5bya
0.7S
Quasi-linear increase through time
feature of main sequence of stellar evolution
73
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?
74
neoarchean S =
0.8S_o
75
deficit in solar forcing balanced with
radiative forcing
CO2
CH4
other GHGs
76
CO2 radiative forcing vs. concentration
50W/m^2 would require 80,000ppm
77
paleosols
fossilized soil in contact w/ atmos., look at mineral assemblage to determine if they could have been present w/ different CO2 levels
78
palaeosols show
10-100pCO2 at 2.5Ga ?
79
Methane radiative forcing
100ppm of CH4 gives 8-15W/m^2, not enough forcing
80
CO2 + CH4 forcing
~40W/m^2-- need another 10
81
the missing F
turn up N2-- pressure broadening
| green line in graphs = 2XN2_atm levels-- CO2 has higher forcing
82
pressure broadening
more molecules = more pressure = more molecular movement (more collisions with radiation)
83
measuring pressure in past
paleobarometer
84
methods for measure pressure in past
fossilized rain drop imprints (tell density)
85
other proposals for 'the other 10'
mixture of other GHGs- ammonia, OCS, clouds
86
clouds
high clouds have strongest greenhouse effect-- more low clouds? -- very unknown
87
when is the cryogenian
650-750Ma, neo-proterozoic (top of the proterozoic)
88
importance of Cryogenian
extensive, Snowball Earth glaciations (pole-pole)
lead into second oxidation event
evolution of animals around this time
89
2 glaciations in cryogenian
1. Sturtian (longer)
| 2. Marinoan
90
pole-pole glaciation
large ice cap instability (past ~30º)
91
sturtian timing
onset: 710-720 Ma
termination: 655-655 Ma
duration: 58Myr
92
Marinoan timing
onset: 640-660Ma
termination: 630-640Ma
duration: 4-14Ma
93
dating glacial onset/termination
O isotopes- get 'reset'
| U-Pb- volcanic ash right below/above glacial sediment
94
sedimentary record of a glacier
glaciers erode and deposit
| produce variety of sediments/structures
95
glacial environment
ice-- out wash plain
| below ice-- glacial till
96
post-glacial environment
till plain-- terminal moraine-- pitted outwash plain
97
till
very poorly sorted sediment ranging in size from very fine grained to giant boulders
98
glacial deposits
```
till
striated clasts
glacial pavement
dropstones
polygonal sand wedges
```
99
glacial pavement
striations/grooves/chattermarks in bedrock
100
chattermark
something in bottom of glacier sticks for a bit then moves.. stick-- move--stick--move
101
dropstone
glacier near body of water-- iceberg-- iceberg drops debris; warp layered beds; can cause folding (if high force)
102
glacial deposits
mostly around glacier margins
103
glacial movement
very dynamic, move all over the place all the time
104
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
105
Importance of glacial deposit present locations
paleogeography, paleomagnetism-- determining where continents were-- determining if glaciation was low latitude
106
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
107
flow/field lines
parallel to surface at equator
| perpendicular to surface at pole
108
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
109
in between glacial units (glacigenic diamictite)
we see carbonate-- implies low latitude
110
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
111
Cryogenian BIFs
reappear in cryogenian after ~1Ga- dramatic drop in oxygen levels ~2-1bya- lower productivity
112
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
113
cap carbonate sequence
pre-glacial carb.-- tillite-- dolomite (dolostone, stromatolites, giant wave ripples, bariite)-- limestone
114
piercing points
align split up formations- large basalt beds, large deformation belts
115
diamictite overlying carbonates
weird, till-cold, carbs-warm
116
commonly seen cap carb 'package'
carb.--diamic--cap carb--carb platform-- diamic--cap--carb--shale--till
117
carbonate platform
low latitude
118
fine sedimentfrom
slow rain out of ice shelf into underlying water
119
cap carb stromatolites
narrower, sharper than usual-- indicate shallow water
120
types of low-latitude glaciation
hard snowball- thick (700m) over all oceans
| open water- slushball, or Jormungand
121
Jormungand
thin belt of water around equator- ablation zone- old ice at tip of glacier- dirty, lower albedo
122
slushball
low-lat continental glaciation but sea-ice instability not reached
123
ice stability graph
stable state at ~10º, some open water
124
initiating a snowball
must lower CO2, reduce GHGs, decrease source, increase sink
125
decreasing GHG source
lower volcanism
126
increasing sinks
weathering, rock formation
127
silicate weathering feedback
negative feedback; temperature dependent; million year timescale
CO2 + CaSiO3--- CaCO3 + SiO2
forward rxn: weathering
backward rxn: metamorphism
128
lichen evolution
increased weathering (acids), photosynthesis, change albedo; CO2 draw down, more nutrients to ocean-- further CO2 drawdown
129
continents were at low latitudes
increasing albedo-- increases Earth albedo (majority of insolation)-- increases weathering
130
Franklin LIP
large basalt eruption, low latitude Large Igneous Province, easily weatherable- large CO2 sink, glaciation driver
131
continental area <15º latitude (%)
~25% at onset of glaciation (~5% 100Ma before that)
132
evidence of increased basalt weathering
Sr isotopes; decreases in 87Sr/86Sr before each of the glaciations
133
solar radiation absorbed
F_SW = (S/S_o)(S_o/4)(1-α)
134
Present day F_SW
239 W/m^2
135
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
136
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) ?
137
300ppmv =
3x10^-4 ppv
| 300x10^-6 ppv
138
deglaciation requires
mean surface T 0ºC
139
∆T =
(alpha)(Forcing)
140
climate models require
0.1bar CO2 to exit snowball earth
141
cap carbonate problem
absence of primary carbonates during glaciation
| fast deposition of thick cap carbonates following deglaciation
142
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
143
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
144
problem with old thinking of cap carbonate problem
most likely some air-sea gas exchange taking place
145
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
146
why no carbonate deposition
lower sea level-- no suitable depositional environment
147
to deposit more carbonate; DIC vs. CO3(2-)
have to move to higher CO3(2-) or lower DIC, generally diagonally down to the right
148
was the ocean acid or neutral during glaciation
2 competing hypotheses
Acid- CO2 influx w/ no Alk flux
Neutral- continued Alk flux
149
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
150
Nitrogen discovered by
Daniel Rutherford, 1772
151
nitrogen rich air
Noxious, Mephitic air
152
how N was discovered
box of air w/ candle, candle absorbs O2, mouse in box, dies
153
N cycles
biologic - fast, dominates in short periods of time
| geologic - slow
154
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
155
nitrogen oxidation states
```
oxidations state and species
V, NO3(-) **abundant
III, NO2(-)
II, NO
I, N2O
0, N2 **
-I, NH2OH
-II, N2H4
-III, NH4 **
```
156
N species most important for ocean biology
NO3
157
N2 in the atmosphere
dominant gas, 78%
158
N as a nutrient
very important, key ingredient in amino acids; triple bond very strong, requires lots of energy, limiting nutrient
159
fixing
breaking triple bond and incorporating N into biomolecules, N2-- NO
160
natural N fixers
lightening (minor)- 5 Tg/yr
| bacteria (major, dominant)- 252 Tg/yr, ~equal btw ocean/land
161
anthropogenic N fixing
Haber-Bosch process
| make NH3 for fertilizer and explosives
162
N is fixed by using
nitrogenase enzyme
| metal cofactors
163
metal cofactors
Fe-Mo (most efficient)
Fe-Fe
Fe-V less efficient
164
N sources before Haber-Bosch
gauno
165
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
166
N fixing reaction
N2-- PN
| particulate nitrogen
167
ammonification
PN-- NH3 or NH4(+)
168
nitrification
NH4(+) --- NO3(-)
| bacterially mediated
169
organisms prefer N in what form
NH4(+)- easiest to incorporate
| NO3(-) is most abundant bioavailable
170
denitrification
NO3(-)---- N2 or N2O
| bacteria using NO3 in electron transport chain
171
largest N flux out of the ocean
denitrification - 240 Tg/yr
| out of balance with input
172
known planets orbiting stars
~2000
173
NASA, Kepler
watches one portion of sky constantly for dips in output radiation of stars (planet going in front of star)
174
beginning of Gaia hypothesis
mars exploration
175
disequilibrium in earths atmosphere
due to life
176
indicate life
persistence of unstable gases in atmosphere
| ex. CH4 only last ~10yrs: ice cores show ~500,000yrs of CH4
177
early mars
features indicative of flowing water but no atmosphere; mars has no plate tectonics; dead planet
178
how to find life
check atmos. composition for equilibrium by using slits to spread light (spectroscopy)
179
what you will see on a planet with no atmosphere
theoretic Planck function
180
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
181
also look for
CO2, O2, O3, CH4
| 'weird' spectrums may equal life
182
a slice in time?
must look at whole earth history-- Archean biosphere had very little O2 even with life
183
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
184
Denitrification ε
= 25‰
| enriches light isotope use-- heavy isotopes left behind
185
denitrification occurs
at boundary between oxic and anoxic layers
186
Tg
10^12
187
δ15N in plants on various substrates
N-rick substrate (schist): δ15N_plant = δ15N_rock
| N-poor substrate (granite): δ15N_plant < δ15N_soil < δ15N_rock
188
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
189
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
190
δ15N and age, vs. [N]
most values are δ15N = 0-10.. for all ages; ~2.4Ga very anomalous- δ15N values from 0-50
191
why was δ15N so high 2.4Ga
the great oxidation-- beginning of nitrification; before 2.4Ga there was no nitrate in the ocean
192
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
193
why Fe, Mo enzyme is 'modern style'
Vnf, Anf, are less efficient and = higher fractionation (more -)
194
Archaen nitrogenase enzyme
Fe-Fe, Fe was very soluble and abundant, Mo was insoluble due to anoxic waters
195
geological N cycles
sedimentation
| hydrothermal alteration
196
N cycle, sedimentation
PN sink-- deposited-- nitrification/denitrification in sed.-- converts to NH4+-- substitutes into clay minerals
197
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
198
N cycle, hydrothermal alteration
new oceanic crust = low N (~1ppm)-- hydrothermal alteration transfers N from O-rocks-- increases concentration up to ~7ppm
199
ocean crust
basalt and gabbro
200
where to look for life
circumstellar habitable zone; not too cold, not too hot, just right
201
boundaries on habitable zone
runaway greenhouse-- hydrogen escape-- ø ---snowball earth-- CO2 condenses
202
early life, exploiting chemical gradients
chemolithoautotrophic– limited by gradients set up in natural environment
203
after great oxidation, life using existing gradients
heterotrophic
photoautotrophic
shift in life– huge earth change– gave life unlimited energy supply
204
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
205
remarkable stable time in Earths history
Holocene, last 10,000yrs
| unprecedented within last few million years
206
climate stability leads to
societal growth
207
climate sensitivity
~3ºC, changes through time
208
climate change scenarios
usually underestimate changes
209
<450ppm CO2
ice on Antarctica
210
>450ppm CO2
no ice anywhere
211
last ppm we will likely see a Holocene like climate
350
212
how to deal with climate change
stop changing things or adapt
213
land surface that is crop land
12%
214
rivers that run dry before they reach the ocean, due to human extraction
25%
215
sources of nitrogen fixation
marine: ~100 ?g/yr
terrestrial: ~100 ?g/yr
industrial Haber-Bosch: ~100 ?g/yr
216
pre-industrial aragonite saturation
3.44
217
carbonate ion concentration
16%
218
effects of anthropogenic N use
eutrophication
219
biggest international transfer of fixed nitrogen
food (shipping crops)
220
Phosphorus use
extraction since pre-industrial has increased by a factor of 20
221
N subduction zones
hot subduction zone- more N volatilized
| cold subduction zone- more N survives past subduction barrier
222
N that makes it past the subduction barrier
possibly sequestered into the mantle
223
calculating N in the mantle
noble gasses
xenoliths and diamonds
experimental petrology
224
N in atmosphere
4x10^18 kg N
225
calculating mantle N w/ noble gasses
Ar, N2 similar behaviour in basaltic melt: measure N2/Ar ratio in basalt- estime N content of mantle
226
MORB N2:Ar
~120
227
OIB N2:Ar
~9300
228
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
229
OIB
ocean island basalt
230
BSE
bulk silicate earth
231
K concentration
280 ±120ppm
| 0.0117% 40K
232
40K decay
10.72%
233
total 40Ar in Earths history
4.2±1.8x10^18 mol
234
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
235
N2 abundance
24±16x10^18 kg N
236
calculating mantle N with xenoliths
find total N = 7x10^18kg in upper mantle; 3X smaller than N2/Ar estimate
237
N is more compatible
under reducing conditions- low oxygen activity, lots of eletrons
238
upper mantle minerals
olivine, pyroxene
239
upper mantle minerals sequester how much N
20 atmospheric masses, mostly in the lowermost upper mantle
240
TZ
transition zone: 410-660km depth
241
LM
lower mantle: ≤660km to core-mantle boundary
242
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.
243
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
244
solution to FYSP?
more N2 in atmosphere makes CO2 a more efficient GHG
245
core N
lots of Fe, N very soluble in Fe
| estimate of amount: 180-300x10^18kg
246
core mass
1.83x10^24kg
247
cornerstone of climate science
Milankovitch hypothesis
248
variations in atmospheric CO2
lag change of global ice volume- insolation variations have a bigger impact than CO2 on ice volume
249
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
250
direct physical connection to insolation variations
rate of change of ice volume dV/dt
251
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
252
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
253
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
254
broadness of physical basis of life
includes flames, vortex motion and others
255
wherever life exists, its biochemical form will be
strongly determined by the initiating event, environment at time of initiation
256
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
257
experiments for detection of life
search for order
| search for non-equilibrium
258
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
259
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
260
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
261
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)
262
Implies oceans are composed of liquid water
high humidities over most of planet
263
why water is an ideal medium for life
dielectric constant, solvation properties, heat capacity, temperature range or liquid state
264
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
265
N2O on Earth
atmospheric life = ~50yrs, non-biological mechanisms are too minuscule to contribute as much as is seen
266
unusual RED spectral imaging
corresponds to no plausible mineral- signature of light-harvesting pigment in a photosynthetic system (chlorophyll a,b)
267
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
268
Bistability of atmospheric oxygen and the great oxidation
Goldblatt, 2006; history of earth = major transitions separated by long periods of relative stability
269
earths largest chemical transition
the Great Oxidation, ~2.4ba; [O2] rose from 0.01PAL
270
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.
271
Great Oxidation =
switch to high oxygen steady state
272
bistability from
UV shielding of troposphere by O3-- nonlinear increase in lifetime of atmospheric O2
273
O2 before life
<10^-12 PAL
274
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'
275
major metabolic pathway before GO
CO2 + H2O + hv––– 1/2CH4 + 1/2CO2 + O2
276
bistability feedback
O2 >2x10^-5PAL–– O3 forms–– decreased CH4 oxidation (reduced O2 sink)–– O2 levels increase–– further O3 formation
277
MIF
mass independent fractionation
