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Student Seminars
Snowball Earth Dmitrij Lisnjak Meißen,
Germany Source Hoffman and Schrag, 2000,
Scientific American
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Contents

• Outline
• Event
• Evidence
• Conclusion

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1. Outline

• Earth's climate is subject to change on various
  timescales
• ancient rock layers are the only clues to
  climate of distant past
• periodic occurance
• changes in the Earth's orbit around the Sun
• height of last glaciation approx. 21,000 years
  ago
• 30 earth surface ice covered
• land glaciers over 2 km thick
• sea level drop by 120 m
• pales compared to events of Neoproterozoic era

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1. Outline

• Neoproterozoic 1000-543 million years ago
• subdivided in Tonian, Cryogenian and Edicarian
  Periods
• glacial deposits in rocks of tropical origin
  (Harland 1964)
• paleomagnetic data
• Snowball Earth events during Cryogenian (600
  MYA)

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2. Event

• solar irradiation 6 weaker
• today 343 W/m² global average
• changes in ocean circulation patterns
• smaller landmasses from supercontinent breakup
• former landlocked areas now closer to sources of
  moisture
• higher precipitation
• more CO2 scrubbed out of atmosphere

• albedo water lt landmasses lt ice/snow
• ice-albedo feedback
• Michail Budykos 2d energy balance climate model
• ice at lattitudes lower than 30 triggers
  runaway freeze

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2. Event

• average global temperature drops to -50C
• average thickness of ocean ice gt 1km
• limited by heat emissions from earth interior
• dry air limits growth of land glaciers
• no removal of volcanic CO2 from atmosphere

• survival of living organisms
• chemolithotrophic ecosystems
• geothermal hotspots
• persistant eggs and spores
• psychrophilic organisms
• photosynthesis can occur under up to 100 m of ice

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2. Event

• for excaping the deep freeze 350-times of today
  CO2 Concentration needed
• slow accumulation of volcanic gases (gt10 MY)
• temperatures reaching melting point at equator
• moisture from sublimation/evaporation feeds
  growth of land glaciers

• enhancers
• resumed evaporation
• open water
• melting in 1000 years

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2. Event

• average global temperature rise to 50C
• extreme greenhouse conditions
• (1000-fold CO2 concentration)
• intense water cycle removes CO2 from atmosphere
• erosion increases
• rapid sedimentation as carbonates

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2. Event

• global climate returns to normal
• repeatetd 4 times (between 750 and 580 MYA)
• continental drift to more polar lattitudes

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3. Evidence
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3. Evidence
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3. Evidence

• widespread glacial deposits
• mixed with banded iron formations
• almost everywhere covered with cap carbonates
• expected consequence of extreme greenhouse
  conditions
• crystal fans indicate rapid accumulation
• rock above and beneath glacial deposits depleted
  in C13
• (relative to volcanic source)
• ? drop in biological production

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4. Conclusion

• Earths climate harbours capacity for extreme
  changes
• Neoproterozoic record point to an extraordinary
  type of climatic event
• Snowball- / Hothouse Earth
• carbon cycle as safety switch
• critical treshlold of ice-cover (30 lattitude)
• may have played an active role in spawning
  multicellular life
• unusual and rapidly changing selective pressures
• no such catastrophic events in more recent
  history
• also no occurance up to 1 billion years before
• each successive glaciation over the last several
  cycles has been getting stronger
• still some 80,000 years away from peak of next
  glaciation

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4. Conclusion

• evidence in part weakly supported
• strictly speculative
• different interpretations
• alternate hypotheses

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Thanks!

• Some say the world will end in fire, Some say in
  ice. From what I've tasted of desire I hold
  with those who favor fire. But if it had to
  perish twice, I think I know enough of hate To
  say that for destruction ice Is also great And
  would suffice.
• -Robert Frost