Co-evolution of life and atmosphere

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Co-evolution of life and atmosphere

• Moving toward a stable Earth

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Bacterial photosynthesis
Green plant photosynthesis
Autotrophs
Sulfate reduction
Oxic respiration
Heterotrophs
Each autotrophic process has counterbalancing
heterotrophic process
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Autotrophy vs. heterotrophy

• Describes where an organism get its C
• Autotrophs get C from CO2 fixation
• Requires external energy source
• Photosynthesis energy from light
• Chemosynthesis energy from chemical bonds
• Autotrophs generally the base of the food chain
• Heterotrophs get C from organic C
• Eat their C
• Energy from chemical bonds

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Energy metabolism vs. electron donor

• Phototrophs light is energy
• Chemotrophs chemical reactions for energy
• Photoautotrophs light is energy and C from CO2
• Photoheterotrophs light is energy and C from
  organic C
• Chemoautotrophs chemical rxns for energy and
  CO2
• Chemoheterotrophs - .
• Lithotrophs inorganic electron donors
  (chemolithotrophs and photolithotrophs)
• Organotrophs organic electron donors
  (chemoorganotrophs and photoorganitrophs)

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Heterotrophs

• Use organic carbon as both carbon and energy
  sources
• Aerobic heterotrophs use O2 as terminal e-
  acceptor
• Anaerobic heterotrophs use nitrate, sulfate,
  carbon dioxide, etc. as terminal e- acceptors
  (many biogeochemically important processes
  including denitrification, sulfate reduction,
  acetogenesis)
• Non-respiratory anaerobes fermentation to
  generate energy and reducing power oxidize
  organic compounds using other organic compounds
  as both the terminal electron acceptor
• Faculative anaerobes switch between
  fermentation and anaerobic respiration

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Respiration

• Done by plants and animals
• Process to convert biochemical energy to ATP
  which a cell can use and waste products
• Involves oxidation of one compound and reduction
  of another
• Aerobic oxidized compound is O2 (terminal
  electron acceptor) reduced compound is glucose,
  some other sugar or amino and fatty acids, etc.
• Anaerobic oxidized compound is something else

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Aerobic respiration

• Heterotrophs need some sort of external electron
  acceptor to oxidize organic C and extract energy
• Oxygen is the most efficient electron acceptor
• Yields the most energy
• Reverse of photosynthesis

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Anaerobic respiration

• Once O2 is depleted, bacteria use other ways to
  extract energy from organic matter oxidation
• Less efficient than aerobic respiration
• Store some energy in reduced end-products
• From evolutionary standpoint, we started at least
  efficient and worked our way up
• Respiration and fermentation are often coupled
  together in the decomposition of complex organic
  matter

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Respiration
Aerobic
Anaerobic/fermentative
ATP is produced cellular energy Oxidation of
organic compounds Oxygen is the terminal electron
acceptor
ATP is produced Oxidation of organic
compounds Other compounds are the terminal
electron acceptors nitrate, sulfate,
carbon dioxide, Fe and Mn oxides
Distribution of metabolic traits has been used to
define them taxonomically
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evolution (?)
energetics
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Fermentation is important to microbes
and people too !!!
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Metabolisms

• Important coupling between elements
• Changes in reactants and byproducts
• Important for balancing elemental cycles

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Organic matter production

• Organic matter produced by autotrophs is more
  than CH2O
• Polysaccharides, proteins, lipids
• Include N (amino acids, proteins, nucleotides)
• Includes P (phospholipids, energy compounds)
• Marine versus terrestrial organic matter
• Marine OM rich in N and P
• Protein very important
• Redfield ratio 106161 (CNP)
• Production and consumption of 1 mole of this
  material produces/consumes 138 moles of O2
• Terrestrial OM rich in C (lignocellulose)
• Different degrees of reactivity some is
  recycled and some is buried and its not random
  usually

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Timing of evolution of metabolisms
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Zircon proof of water

• Common in granites
• Rare in mafic rocks
• Resistant to mechanical and chemical weathering
  so persists in sediments
• Resistant even to metamorphism!
• Contains uranium and thorium so important for
  radiometric dating
• Used as protolith indicators
• Oldest zircons are 4.4 bybp (Australia)
• Oxygen isotopes indicate presence of liquid water

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Oxygen in early atm (Hadean early Archaen)

• Small amounts of O2 from photolysis
• Early oxic ps possible?
• Photodissociation of water vapor to produce O2
  and H2
• H2O hv ? H2 O2
• H2 lost to space
• Photolysis could lead to loss of all water
• Dead oxidized planet? E.g., Venus, more later
• Retention of water on earth crucial and related
  to CO2 retention

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Where did the oxygen go?

• Biological O2 production began 2.7 bybp
• No accumulation of O2 until 2.3 bybp
• Reasons not well understood
• Requires a change in relationship between sources
  and sinks (inputs and exports)
• If sinks gt sources then O2 does NOT accumulate
• Sinks consume all O2 produced
• Once source gt sink, O2 can accumulate
• Sinks decrease over time (sources constant)
• Sources increase over time

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O2 consumption in Archaen

• Oxidation of reduced substances
• Large O2 sinks early on
• Reduced Fe and S
• Reduced mantle components and gasses
• Swamp out oxygen sources
• Leads to no net accumulation at first
• Likely that O2 production by PS also increased
  over time during this period

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Evidence of O2 sinks

• Banded Fe formations (BIFs)
• Alternating layers of silica and Fe-rich minerals
• Fe(II) reduced and soluble
• Fe(III) oxidized and insoluble (ppt out of
  solution)
• Almost exclusively formed prior to 1.9 bybp
• Source of O2 not well-understood
• Can be taken as evidence of changing atm (cant
  infer O2 content of atm)
• Detrital uraninite and pyrite
• Reduced minerals oxidized during weathering so
  see oxidized forms today
• Disappear around 2.2 bybp due to weathering
• Consistent with rise of atm O2
• Atm O2 must have crossed some threshold (0.005
  PAL) around time of their disappearance

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More evidence

• Paleosols (ancient soils) and redbeds Australia
• Reduced Fe is soluble and so paleosols older than
  2.2 by are Fe depleted
• Requires higher O2 than for BIFs
• Sulfur isotopes fractionation in oxic versus
  anoxic atm (see previous)
• Change in patter of fractionation 2.3 2.45
  bybp
• Rocks older than 2.45 bybp show mass-independent
  fractionation
• Younger rocks have well-defined and predicted
  mass-dependent fractionation
• Related to presence of atm O2
• Mass independent fractionation only in atm
• Reactions in liquids or solids are mass-dependant
• In oxic atm, S is oxidized and rains out

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Evolution of Ozone

• Accumulation of free O2 in the atm also led to
  the accumulation of ozone
• Ozone important for blocking incoming UV
  radiation
• Catalytic cycles produce and consume ozone in the
  atm
• Attenuates solar energy flux between 180 320 nm
• Even small amounts of atm O2 leads to enough
  ozone to provide some protection against UV
• Partial screen likely to have formed 1.9 bybp
• Presence of this UV filter allowed life to move
  out of the oceans and onto land
• Consistent with the timing of evolution of
  eukaryotes and higher plants

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Incoming radiation O3 absorption of short l
Ozone prdn.
Ozone destr.
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1.9 bybp
Fig. 11-16 Ozone column depth at different
atmospheric O2 levels.
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Rapid rise in O2 2.3 2.4 bybp Great
Oxidation Event
Cambrian
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More gradual increase in O2 after GOE, well below
present atm Levels (PAL) until Cambrian and
variable since then
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Different O2 requirements for different processes
gt0.15 PAL
Banded iron formations
1.9 Ozone screen established
Redbeds
2.2
2.3
0.01 - 0.005 PAL
Detrital pyrite and uraninite
2.7 Evolution of oxygenic photsynthesis
- biological O2 production begins
lt10-5 PAL
S isotopes
Evolution of anoxygenic photosynthesis
3.5 Life originates (perhaps earlier)
- hyperthermophiles, methanogens
Atmosphere likely CO2 rich Oceans begin to form
Fig. 10-1
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Paradox of the faint young sunHow was the planet
not frozen?

• Initial sun was likely 75 as bright as today
• This solar luminosity with present atm
  composition would have led to a frozen earth
  until 1.9 bybp
• Ancient metamorphosed sediments back to 3.8 bybp
  imply running water (so couldnt have been
  frozen)
• Zircon data pushes date of running water to 4.4
  bybp
• Interior Earth heat from radioactive decay? Not
  enough to make up the difference
• Suggests there must have been super-greenhouse
  to keep temperatures warm
• CO2 and CH4 are likely candidates

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Note Te and Ts based on present-day atmospheric
composition
Solar luminosity curve
Ts below freezing!
Tg
Fig. 12-2
Fig. 12-2 The paradox of the faint young Sun.
Assume constant CO2 Assume constant albedo
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Changes in CO2 with time

• CO2 initially important
• Methane increasingly important in the Archaen
  after life forms
• Methane production from microbes
• Production by methanogens greater than abiotic
  production
• Could have been 1000 ppm or more
• Oxidation by O2 not significant in early atm

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• Move C to rock reservoir
• Onset of weathering, widespread CaCO3 ppt.,
  origin of life

• Archean

• Hadean

Present day
CO2 concentrations necessary to compensate for
changes in solar Luminosity (with only H2O and
CO2 greenhouse gases)
Fig. 12.3
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Temp curves shift up with increasing methane
More CO2 not necessary to maintain habitable
surface temps if there Was more CH4
Atmos CO2 upper limit from paleosol data
Need to stay above this so as not to freeze
Freezing point of water
Hadean/early Achaean (up to 1-10 bar)
present-day CO2
Fig. 12-4 Average surface temperature as a
function of atmospheric CO2 and CH4
concentrations.
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Siderite absent from late Archean paleosols

• Siderite (FeCO3) should be there if CO2 was
  higher
• Set upper limit for atmospheric CO2
• Combined with the freezing point of water,
  constrains atmospheric gas content
• Suggests CO2 levels could have dropped
  significantly by late Archaen
• Methane and CO2 possibly of equal importance as
  atm components that led to the needed
  super-greenhouse

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Why the drop in Atm CO2

• Weathering, calcium carbonate ppt, and the origin
  of life would have all removed CO2 from the
  Archaen atmosphere
• Amount of C in sed rocks as OM and CaCO3 may have
  been close to present day value by late Archaen
• Active plate tectonics did not start until early
  Proterozoic
• Dont have a complete carbonate-silicate cycle
• Effective CO2 removal from the atm (weathering)
  without as efficient replacement (subduction,
  melting and return of sedimentary C)

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The carbonate/silicate cycle in the early Archaean
Atm. CO2 loss in the Archean
X
CO2
Uptake into organic matter
CO2
CO2
Weathering of silicate rocks
Ions (and silica) carried by rivers to oceans
Ca2 2HCO3- ( SiO2aq)
Organisms build calcareous (and siliceous) shells
SiO2
CaCO3 CO2 H2O ( SiO2(s)
CO2
Subduction (increased P and T)
CaCO3 SiO2 ? CaSiO3 CO2
CaSiO3 2CO2 H2O ? Ca2 2HCO3- SiO2
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Archaen Methane

• Production has potential to develop a positive
  feedback loop high temp, more methane
  production, etc.
• High methane also leads to an anti-greenhouse
  effect avoiding runaway warming
• Due to polymerization of CH4 to hydrocarbons
• Orange haze (Titan) due to Mie scattering when
  light of similar l to particle size
• Anti-greenhouse effect as CH4 absorbs red l high
  in atm so it doesnt reach surface
• Feedback mechanisms involving atm CO2 and methane
  and Archaen climate control
• Methane production biologically driven (so could
  be Gaian in nature)

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Most methanogens are hyperthermophiles
Runaway warming
Fig. 12-5
Fig. 12-6
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Breakdown of Archean climate control

• Evolution of oxygenic ps enhances oxidation of
  methane by O2
• Decrease in methane production
• Low methane and CO2 decrease greenhouse effect
• Coincides with first documented glaciation on
  Earth (Huronian glaciation)
• Development of plate tectonics completes
  carbonate-silicate cycle
• Leading to long-term climate regulation by CO2
• Rebound from global glaciation event

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adds back CO2
Onset of modern plate tectonics turns this on
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Maintaining habitable climate

• Low methane levels and the ability to control CO2
  despite increasing solar luminosity
• Relative contribution of geochemical versus
  biological process in maintaining this balance?
• How do the feedback mechanisms work?

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Long-term climate regulation

• Climate stabilization broke down at beginning and
  end of Proterozoic
• Huronian glaciation (2.3 bybp) rise of atm O2
  displacing CH4
• Invoke carbonate-silicate cycle negative feedback
  to end this
• Neoproterozoic Snowball Earth entire oceans
  may have frozen (0.8 0.6 bybp) atm CO2 drawn
  down to low levels
• Phanerozoic oscillated between hot houses and
  cold houses
• Long-term carbonate-silicate system modulated by
  other factors
• Biological processes and organic C burial
• Changes in tectonic activity
• Periods of rapid seafloor spreading high CO2
• Periods of slower seafloor spreading low CO2
  and deeper basins
• Cooling in mid-Cenozoic may be related to changes
  in weathering rates

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Snowball Earth Continents clustered in
tropics CO2 drawdown Continued weathering b/c
of continent location More drawdown Albedo
effects from growing ice sheets Freezing of
earth Stops weathering Stops CO2 drawdown .
Neoproterozoic Snowball Earth
Huronian Glaciation (2.5-2.3 bybp)
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Liquid water/moderate temperature

• Provides the medium for geochemical cycles
• Cycles elements needed for life
• Implies a reasonable ambient temp on the planet
  (not Venus)
• May be related to the ability of the Earth system
  to initially sequester atm CO2 in crustal rocks
• Development of feedback loops controlling CO2
• Other greenhouse gases of importance (CH4 and
  N2O)
• Produced by anoxic microbial processes
• Methanogenesis and denitrification
• As Earth evolved from anoxic to oxic environ,
  cycles of these gases probably played a role in
  fine-tuning climate regulation

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Venus

• Runaway greenhouse
• Similar size,density and internal heat flow
• Probably started out with similar amounts of H2O
  and CO2
• However on Earth, most of the CO2 is locked up as
  limestone or sedimentary OM
• On Venus, it remained in atmosphere
• So surface temperatures of Venus much hotter (gt
  400oC)

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Venus

• Earths IR flux/temperature feedback an important
  negative feedback controlling climate
• On Venus, early breakdown in that feedback
• Feedback can break down if atm contains too much
  H2O
• If you never hit the water vapor line it never
  rains
• Atm continues to gain H2O (as vapor)
• Greenhouse effect continually increases
• Increasing surface temp does not lead to enhanced
  IR flux at top of the atm (loss of radiation from
  atmosphere)
• Traps heat (radiation) more effectively
• Happened on Venus during early history?
• Closer to the sun
• Solar flux greater than that to present-day Earth
  (even when sun was dimmer

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Fig. 3-22
Curvature driven by water vapor feedback on
greenhouse effect
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Runaway warming

• Atm becomes warm and full of water vapor
• Negative feedback breaks down (runaway
  greenhouse)
• Photolysis in upper atm led to loss of water
• H2 lost to space, O2 reacts with reduced Fe in
  crustal material or reduced gases in the atm
• Atm on Venus now only has traces of H2O
• Lack of H2O inhibits weathering and volcanic CO2
  accumulates
• Volcanic S gases also accumulate as sulfuric acid
• Hot dry planet with a thick, CO2-rich atm

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Fig. 19-2 Systems diagram illustrating the
runaway greenhouse on Venus.
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5. CO2 increases in the atmosphere
4. Loss of water decreases silicate weathering
3. Photolysis of water in upper atmosphere
2. Warm atmosphere fills with water vapor
1. Positive feedback between water vapor and
temperature
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Mars

• Start colder because smaller solar flux
• CO2 condenses out (but no return mechanism no
  active plate tectonics)
• Small size means smaller internal radioactive
  heat source
• Shuts down carbonate-silicate cycle (and return
  mechanisms)

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Earth the perfect storm

• Earths retention of water and trapping of CO2 in
  the crust avoided runaway greenhouse
• Led to rapid decrease in atm CO2 during the
  Archaen
• ppt of CaCO3
• OM formation
• Role of life?

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Later evolution

• O2 in atm allowed evolution of more complex
  organisms
• Eukaryotes, plants, and animals (other half of
  tree)
• Mass extinction events also important in the
  evolutionary process
• Several major mass extinction events
• End of Permian largest event
• End of Cretaceous (K-T boundary)
• Extinction of dinosaurs
• Allowed for evolution of mammals
• May have been meteor impact
• Caused by variety of factors
• Biological, geological, extra-terrestrial

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Later evolution

• Eukaryotes present in fossil record 2.7 bybp
• Multicellular organisms appear in the fossil
  record only 560 mybp
• Cambrian explosion 544 mybp
• O2 in atm allowed evolution of more complex
  organisms
• Eukaryotes, plants, and animals (other half of
  tree)
• Burial of organic C resulted in rapid O2
  production
• Large burial event along with rapid rise in O2
• Isotopically light sedimentary organic C due to
  ps

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Fires and Atm O2

• Range of O2 concentrations allow modest fires
  13-35
• O2 concentrations stable within this range for
  some time
• Have a record of fires (charcoal) since the late
  Devonian period (365 mybp)
• Lower bound O2 concentration of 13 below which
  fires can not ignite
• Upper bound O2 concentration of 35 would
  destroy earths biota
• After K-T impact event?

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Controls on Atm O2?

• Photosynthesis versus burial of organic C
• Negative feedback (purely hypothetical as data
  dont show this)
• Cold waters have high O2 and sink to make deep
  water
• This would allow more respiration of sinking C
• Consume O2
• Deplete oceanic O2
• Lower O2 would allow more C burial (less
  respiration)
• Negatively feeding back on and stabilizing
  atmospheric O2

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CO2 consumed
Cooling related to changes (incr.) in weathering
rates (?)
Cooling related to increased carbon burial
Neoproterozoic Snowball Earth
Huronian glaciation
Burial
Rise of atm O2 around 2.3 by would have
eliminated the atm CH4 and caused temporary
cooling? Detrital uraninite below indicate low
atm O2 above is redbed which was formed under
high O2. Then a jump in CO2 to cause warming or
recovery of atm CH4?
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Atmospheric stability

• Mesozoic warming (251 65 mybp)
• Higher atm CO2
• Isotopic evidence
• Rapid sea floor spreading (magnetic patterns)
• CO2 production from carbonate metamorphism
  outgassing at spreading centers
• Low latitudnal heat gradient equator-pole
• Ocean-atm circulation phenomenon?
• Late Cenozoic cooling 80 mybp
• Decrease in spreading rates
• Perturbation in carbonate-silicate cycle due to
  collision of India with Asia?

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Back to life -Darwins main points

• In any population, more offspring are produced
  that can survive to reproduction
• Genetic variation occurs in populations
• Some inherited traits increase the probability of
  survival
• Bearers of those traits are more likely to leave
  offspring to the next generation those traits
  accumulate
• Environmental conditions determines which traits
  are favorable

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Evolution and the Modern Synthesis

• DNA can be changed by random mutations
• Mutations give rise to different traits
• Traits can be acted upon by natural selection
• Many unanswered questions
• How did major taxonomic groups arise?
• What was the source of mass extinctions?

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Extinctions

• A major selective force in evolution?

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Six major mass extinctions in Earth History

• Geologic Period MYA Percent Extinct
• Late Ordovician 435 27
• Late Devonian 365 19
• Late Permian 245 57
• Late Triassic 220 23
• Late Cretaceous 65 17
• Late Eocene 35 2
  

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Cretaceous extinction probably caused by an
impact somewhere near Yucatan

• Led to
• Extinction of the dinosaurs
• Extinction of 17 of marine fauna
• Rise of the mammals

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Role of life processes in modern day global cycles

• Present day controls on O2 in the atmosphere
• Evolution of life has led to an oxidizing
  environment on Earths surface
• Present day O2 level controlled by balance
  between PS and C burial
• CO2 H2O lt-gt CH2O O2
• Bury OM in seds and leave O2 in the atm not
  decomposed
• Carboniferous period
• More complex see book
• Other feedback mechanisms help control
  large-scale excursions in O2 and CO2
  concentrations

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Earth system

• We can think of Earth to have a reducing core and
  oxidizing crust
• Without external forcing of continued PS, this
  couldnt exist
• Life harvests solar energy and uses it to
  maintain this disequilibrium between core and
  crust
• Ability of life to sequester solar input is very
  important

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The Elements of Life

• In addition to energy, life requires certain
  material substances
• All organisms require 23 basic elements
• Availability of these elements can limit growth
  and survival

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Modern Biogeochemical Cycles

• Elements cycle between organisms, the water, the
  sediments and the land
• The maintenance of life requires continued access
  to these elements
• Only a few are of biogeochemical significance
• C, N, P, Si, Fe
• Elemental ratios in living organisms are fairly
  constant
• Marine systems Redfield Ratio CNP 106161

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Next time

• Present day global cycles
• Atmosphere
• Chapter 4
• Ocean
• Chapter 5