How Stable is Planet Earth

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The major transitions of Gaia
Tim Lenton, Richard Boyle, Colin Goldblatt,
Hywel Williams, Andy Watson School of
Environmental Sciences, University of East
Anglia, Norwich, UK
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Outline

• The origin of Gaia
• The Great Oxidation
• The Neoproterozoic

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Gaia theory

• The system as a whole self-regulates climate and
  chemistry in a habitable state

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Gaia theory

• The system as a whole self-regulates climate and
  chemistry in a habitable state

Gyr ago
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Gaia theory

• The system as a whole self-regulates climate and
  chemistry in a habitable state
• There have been a series of habitable states
  separated by major transitions

Gyr ago
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Gaia theory

• The system as a whole self-regulates climate and
  chemistry in a habitable state
• There have been a series of habitable states
  separated by major transitions

Great oxidation
Extreme glaciations
Reducing atmosphere
Environment
Gyr ago
8
Gaia theory

• The system as a whole self-regulates climate and
  chemistry in a habitable state
• There have been a series of habitable states
  separated by major transitions

Great oxidation
Extreme glaciations
Reducing atmosphere
Environment
Gyr ago
Origin of life
Photo- synthesis
Animals
Eukaryotes
Life
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Gaia theory

• The system as a whole self-regulates climate and
  chemistry in a habitable state
• There have been a series of habitable states
  separated by major transitions
• Life can drive major transitions

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Environment
Ages in Ga (109 yr BP)
Life
T. M. Lenton et al. (Working Group 1) 91st Dahlem
Workshop on Earth System Analysis for
Sustainability (2003)
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Carbonate isotopic composition
Shields and Veizer (2002)
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Origin of life (gt3.5Ga)

• Anoxygenic photosynthesis
• Limited by substrate
• How readily did recycling and regulation emerge?

3.5Ga Stromatolite, Barberton, S. Africa
Modern Stromatolite, Hamelin Pool, Australia
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Emergence of nutrient recycling
The Flask model
Williams Lenton (2007) Oikos
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Emergence of nutrient recycling
The Flask model
Nutrient input
Nutrient output
Williams Lenton (2007) Oikos
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Emergence of nutrient recycling
The Flask model
Nutrient input
Abiotic variables
Nutrient output
Williams Lenton (2007) Oikos
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Emergence of nutrient recycling
The Flask model
Nutrient input
Abiotic variables
Seeded with clonal population of microbes
Nutrient output
Williams Lenton (2007) Oikos 116 1087-1105
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Emergence of nutrient recycling
The Flask model
Nutrient input
Abiotic variables
Recycling Ratio
Time
Population diversifies
Nutrient output
Williams Lenton (2007) Oikos 116 1087-1105
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Emergence of nutrient recycling
The Flask model
Nutrient input
Abiotic variables
Recycling Ratio
Time
Recycling population expands
Population
Nutrient output
Williams Lenton (2007) Oikos 116 1087-1105
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Emergence of environmental regulation
Spatial system of flasks connected in a ring
Measure the Error Mismatch between the state
of the abiotic environment and the organisms
preference
Vary the rate of mixing between the flasks
Here we use fixed, universal preferences
Williams Lenton (in prep.)
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Emergence of environmental regulation
Spatial system of flasks connected in a ring
Environmental Error
Time
Measure the Error Mismatch between the state
of the abiotic environment and the organisms
preference
Vary the rate of mixing between the flasks
Here we use fixed, universal preferences
Williams Lenton (in prep.)
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Emergence of environmental regulation
Spatial system of flasks connected in a ring
Environmental Error
Time
Measure the Error Mismatch between the state
of the abiotic environment and the organisms
preference
Mean Error
Extinctions
Vary the rate of mixing between the flasks
Here we use fixed, universal preferences
Mixing rate (log scale)
Williams Lenton (in prep.)
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Mechanism of regulation (1)
Williams Lenton (in prep.)
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Mechanism of regulation (2)
Example of situation below E-
Environment-improving ecosystem
Environment-degrading ecosystem
Net transfer of organisms
Large population
Small population
Larger populations are better colonisers of
available space and this gives rise to
higher-level selection The spread of
environment-improving ecosystems alters the
global environment toward optimal conditions
Williams Lenton (in prep.)
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Oxygenic photosynthesis (gt2.6Ga)

• Unlimited free-energy capture
• CO2 drawn out of atmosphere
• CH4 returned by methanogens
• Organic carbon buried in crust
• O2 consumed in oxidising CH4, organic carbon and
  reduced inorganic material
• H loss to space

Modern cyanobacteria Anabaeana scheremetievi
2 Ga cyanobacteria? Eoentophysalis belcerensis
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History of atmospheric oxygen
PAL Present Atmospheric Level
Great oxidation
Origin of life
Oxygenic photosynthesis
Goldblatt, Lenton, Watson (2006) Nature
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Mass Independent Fractionation (MIF) of sulphur
indicates O2 lt 10-5 PAL
Ozone layer present
Great Oxidation
Oxygenic photosynthesis
Goldblatt, Lenton, Watson (2006) Nature
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Bi-stability of atmospheric oxygen
Steady states are separated by formation / loss
of an ozone layer
Goldblatt, Lenton, Watson (2006) Nature
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Bi-stability of atmospheric oxygen
Oxidised soils lt2.2 Ga
MIF of Sulphur gt2.4 Ga
Goldblatt, Lenton, Watson (2006) Nature
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Bi-stability of atmospheric oxygen
gt2.4 Ga global Fe input
Present hydrothermal Fe input
2.69-2.44 Ga Hamersley BIF Fe deposition
Time (Ma)
Goldblatt, Lenton, Watson (2006) Nature
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The Great Oxidation

• Potential triggers
• A decline in reductant input from the mantle
• An increase in net primary productivity
• A pulse of organic carbon burial
• Could be a combination of the above

Goldblatt, Lenton, Watson (2006) Nature
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The Great Oxidation

• A small biological or geological perturbation
  could have caused the major transition
• Once it occurred it was difficult to reverse
• It facilitated the evolution of eukaryotes
• It was associated with extreme glaciations

1.6 Ga probable eukaryotic alga Grypania
spiralis 2cm diameter coils
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Oxygen and glaciations
Second oxygen rise
Great oxidation
The boring billion (or so)
PAL Present Atmospheric Level
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Snowball Earth events

• 2220 Ma (Makganyene), 710Ma (Sturtian) and
  640Ma (Marinoan)

• Runaway positive feedback
• Switch between quasi-stable states

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Multiple stable states for ice cover
Present
Neoproterozoic
Budyko / Sellers (1969) Energy Balance Model
Based on Hoffman (2002)
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Hypothesised trigger Land colonisation
Fungi 1430 Ma
Algae 750 Ma
Lichens 600 Ma
Cyanobacteria 850 Ma
Butterfield (2005) Paleobiology 31 165-182 House
et al. (2000) Geology 28 707-710 Butterfield
(2004) Paleobiology 30 231-252 Yuan et al.
(2005) Science 308 1017-1020

• Microfossils
• Molecular clocks
• Carbon isotope signature of photosynthetic
  microbial communities

Heckman et al. (2001) Science 293 1129-1133
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Consequences of bio-weathering

• Silicates ? Carbonates
• Decrease in CO2
• Snowball Earth events
• 0.74 Ga
• 0.59 Ga
• Phosphorus ? Organic C
• Increase in O2
• Necessary for larger animals
• Ediacara 0.57 Ga
• Cambrian explosion 0.54 Ga

Lenton Watson (2004) Geophys. Res. Lett. 31
L05202
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Why the rise of animals?

• Increase in atmospheric oxygen was necessary but
  not sufficient
• Terminal differentiation of cells in a
  multi-cellular animal is highly altruistic
• Hypothesis Extreme glaciations favoured the
  evolution of altruism

Boyle, Lenton Williams (2007) Geobiology
560 Ma Ediacaran Dickinsonia 10cm diameter
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Snowball Earth Life in refugia
Normal conditions High dispersal
C
C
A
A
A
A
C
A
C
A
C
C
C
C
A
A
C
C
C
C
A
A
A
A
Boyle, Lenton Williams (2007) Geobiology
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Snowball Earth Life in refugia
Normal conditions High dispersal
C
A
A
C
A
C
C
A
C
C
A
A
Boyle, Lenton Williams (2007) Geobiology
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Snowball Earth Life in refugia
Normal conditions High dispersal
C
A
A
C
A
C
C
A
C
C
A
A
Time
A
A
A
A
Cheats kill the groups they are in and cannot
spread elsewhere
Extreme founder effects increase relatedness and
within-group kin selection for altruism
C
A
A
A
Boyle, Lenton Williams (2007) Geobiology
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Snowball Earth Life in refugia
Normal conditions High dispersal
C
A
A
C
A
C
C
A
Altruist frequency
C
C
Surviving groups
A
A
Time
A
A
A
A
C
A
A
A
Boyle, Lenton Williams (2007) Geobiology
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Conclusion

• The evolution of life had a role in causing major
  transitions of Gaia
• Geophysical and geochemical forcing factors and
  feedbacks were also important
• Each transition was contingent on the previous
  one and had profound consequences for evolution
• Life may have inadvertently pushed the bounds of
  habitability (several times)
• The (re-)emergence of environmental regulation is
  a robust feature of our model virtual worlds

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Earth as seen from Galileo spacecraft 11 December
1990
Source NASA