Snowball Earth

Snowball Earth

Presented by Mindi Purdy and Jen Ulrich

Theory of Snowball EarthTheory of Snowball Earth• Many lines of evidence support a theory that Many lines of evidence support a theory that

the entire Earth was ice-covered for long the entire Earth was ice-covered for long periods 600-700 million years ago.periods 600-700 million years ago.

• Each glacial period lasted for millions of Each glacial period lasted for millions of years and ended violently under extreme years and ended violently under extreme greenhouse conditions.greenhouse conditions.

• Proposes that these climate shocks triggered Proposes that these climate shocks triggered the evolution of multicellular animal life and the evolution of multicellular animal life and challenge long-held assumptions regarding challenge long-held assumptions regarding the limits of global change.the limits of global change.

What Evidence Supports the What Evidence Supports the theory of Snowball Earththeory of Snowball Earth

• Sun’s radiation/Earth’s AlbedoSun’s radiation/Earth’s Albedo• Glacial DepositsGlacial Deposits• PaleomagnetismPaleomagnetism• Carbon DioxideCarbon Dioxide• IsotopesIsotopes• Evolutionary burstEvolutionary burst

Sun StrengthSun Strength• Main sequence Main sequence

starsstars: : radiate more radiate more energy as their energy as their helium cores grow helium cores grow more massive.more massive.

• The sun’s luminosity The sun’s luminosity in the in the Neoproterozioc Neoproterozioc period was only 93% period was only 93% - 94% of its present - 94% of its present value (Hoffman).value (Hoffman).

Heat BalanceHeat Balance

• The earth’s surface temperature is The earth’s surface temperature is governed by the heat balance governed by the heat balance between incoming solar radiation between incoming solar radiation and outgoing radiation emitted by and outgoing radiation emitted by surface or near surface. surface or near surface.

• In layman’s terms: In layman’s terms: heat absorbed heat absorbed should equal heat emittedshould equal heat emitted

Heat BalanceHeat BalanceRR22EEss(1-(1-)=4)=4RR22(f(fTTss

44))

• R is the planetary radius R is the planetary radius • EEss is the solar irradiance is the solar irradiance is the planetary albedo is the planetary albedo • f is the effective infrared transmission f is the effective infrared transmission

factor (greenhouse effect) factor (greenhouse effect) is the Steffan Boltzman constant is the Steffan Boltzman constant

(5.67 x 10(5.67 x 10-8-8 Wm Wm-2-2 x K x K-2-2) ) • TTss is the surface temperature is the surface temperature

(Hoffman).(Hoffman).

AlbedoAlbedo• Planetary albedo is defined as the Planetary albedo is defined as the

fraction of incoming radiation that is fraction of incoming radiation that is reflected back to space. It could also reflected back to space. It could also be considered in terms of the degree be considered in terms of the degree of whiteness.of whiteness.

• So according to the formula, if the So according to the formula, if the planetary albedo where to increase, planetary albedo where to increase, what would happen to surface what would happen to surface temperatures?temperatures?

RR22EEss(1-(1-)=4)=4RR22(f(fTTss44))

AlbedoAlbedo

Ice-Albedo FeedbackIce-Albedo Feedback• For any For any

imposed imposed cooling, the cooling, the resulting resulting higher albedo higher albedo would cause would cause further cooling. further cooling. This positive This positive feedback also feedback also applies to applies to warming. warming.

Runaway Ice AlbedoRunaway Ice Albedo

• If Earth’s climate cooled, and ice If Earth’s climate cooled, and ice formed at lower and lower latitudes, formed at lower and lower latitudes, the planetary albedo would rise at a the planetary albedo would rise at a faster and faster rate because there faster and faster rate because there is more surface area per degree of is more surface area per degree of latitude as one approaches the latitude as one approaches the equator (Hoffman). equator (Hoffman).


• In a simulation done by Budyko, once In a simulation done by Budyko, once ice formed beyond a critical latitude ice formed beyond a critical latitude (30(30 North or South- half of the North or South- half of the Earth’s surface area), the positive Earth’s surface area), the positive feedback became so strong that feedback became so strong that temperatures plummeted and the temperatures plummeted and the entire earth froze over (up to 1 km entire earth froze over (up to 1 km thick in oceans).thick in oceans).

First CluesFirst Clues• Thick layers of ancient rock hold Thick layers of ancient rock hold

clues to climate of Neoproterozoicclues to climate of Neoproterozoic– Occurrence of glacial debris near sea Occurrence of glacial debris near sea

level in tropics?level in tropics?– Unusual deposits of iron-rich rock should Unusual deposits of iron-rich rock should

only form when there is little to no only form when there is little to no oxygen in the oceans and atmosphere.oxygen in the oceans and atmosphere.

– Rocks known to form in warm water Rocks known to form in warm water seem to have accumulated right after seem to have accumulated right after glaciers receded.glaciers receded.

• Nambia’s Skeleton CoastNambia’s Skeleton Coast– Provides evidence of glaciers in rocks Provides evidence of glaciers in rocks

formed from deposits of dirt and debris formed from deposits of dirt and debris left behind when ice melted. left behind when ice melted.

– Also found rocks dominated by calcium and magnesium just above debris. just above debris.

– Chemical evidence that a hothouse Chemical evidence that a hothouse could have followed.could have followed.

• 1964, Brian Harland pointed out that 1964, Brian Harland pointed out that glacial deposits dot Neoproterozoic glacial deposits dot Neoproterozoic rock outcrop virtually every continent.rock outcrop virtually every continent.

• Joseph Kirschvink promoted Joseph Kirschvink promoted Neoproterozoic deep freeze because Neoproterozoic deep freeze because of iron deposits found mixed with of iron deposits found mixed with glacial debris.glacial debris.– Millions of years of ice could readily Millions of years of ice could readily

create this situation. Therefore dissolved create this situation. Therefore dissolved iron expelled from seafloor hot springs iron expelled from seafloor hot springs could accumulate in water.could accumulate in water.

Carbonate CluesCarbonate Clues• Neoproterozoic blanketed by carbonate Neoproterozoic blanketed by carbonate

rocks which form in warm shallow seas.rocks which form in warm shallow seas.• Transition from glacial deposits to cap Transition from glacial deposits to cap

carbonates abrupt and lacks evidence carbonates abrupt and lacks evidence significant time passedsignificant time passed

• Thick sequence of extreme greenhouse Thick sequence of extreme greenhouse conditions unique to transient aftermath conditions unique to transient aftermath of Snowball Earth.of Snowball Earth.

Banded iron-formation with Banded iron-formation with ice-rafted carbonate dropstone ice-rafted carbonate dropstone

in Mackenzie Mtns, Canada in Mackenzie Mtns, Canada

Critical Element: Location of Critical Element: Location of the Continentsthe Continents

• Harland’s idea based on assumption that Harland’s idea based on assumption that continents were all located near the equator continents were all located near the equator during the Neoproterozoic period.during the Neoproterozoic period.

• ReasoningReasoning– When continents near poles, CO2 in atmosphere When continents near poles, CO2 in atmosphere

remains high enough to keep planet warm.remains high enough to keep planet warm.– If continents cluster in tropics, they would remain If continents cluster in tropics, they would remain

ice-free as the earth grew colder and approached ice-free as the earth grew colder and approached critical threshold for Runaway freeze.critical threshold for Runaway freeze.

– In other words, the CO2 “safety switch” would fail In other words, the CO2 “safety switch” would fail because carbon burial continues unchecked.because carbon burial continues unchecked.

• Harland’s EvidenceHarland’s Evidence– Paleomagnetism Paleomagnetism

•uses the alignment of magnetic minerals in uses the alignment of magnetic minerals in rock deposits (termed natural remnant rock deposits (termed natural remnant magnetization) to determine where the magnetization) to determine where the deposits were formed.deposits were formed.

•Before rocks harden, grains aligned Before rocks harden, grains aligned themselves with magnetic field.themselves with magnetic field.

– If formed near poles, magnetic orientation If formed near poles, magnetic orientation would be nearly verticalwould be nearly vertical

– Instead found the grains dipped only Instead found the grains dipped only slightly relative to horizontal because of slightly relative to horizontal because of their position near the equatortheir position near the equator..

• Carbon Dioxide absorbs infrared radiation Carbon Dioxide absorbs infrared radiation emitted from the Earth’s surface.emitted from the Earth’s surface.

• Key to reversing Runaway freezeKey to reversing Runaway freeze• It is emitted from volcanoesIt is emitted from volcanoes

– Offset by erosion or silicate rocksOffset by erosion or silicate rocks•Chemical breakdown of the rocks converts Chemical breakdown of the rocks converts

CO2 to bicarbonate and is washed into CO2 to bicarbonate and is washed into oceans.oceans.

•Bicarbonate combines with Calcium and Bicarbonate combines with Calcium and Magnesium ions to produce carbonate Magnesium ions to produce carbonate sediments.sediments.

• Joseph Kirschvink pointed out that during Joseph Kirschvink pointed out that during Snowball Earth shifting tectonic plates Snowball Earth shifting tectonic plates would continue to build volcanoes and to would continue to build volcanoes and to supply the atmosphere with CO2.supply the atmosphere with CO2.

• At same time liquid water needed to At same time liquid water needed to erode rocks and bury Carbon is trapped erode rocks and bury Carbon is trapped in ice.in ice.

• Eventually CO2 level would get high Eventually CO2 level would get high enough that it would heat up planet and enough that it would heat up planet and end Snowball Earth.end Snowball Earth.

• Kenneth Calderia and James Kasting Kenneth Calderia and James Kasting estimated to overcome a runaway estimated to overcome a runaway freeze it would require roughly 350 freeze it would require roughly 350 times present day concentration of times present day concentration of CO2.CO2.

• Once melting begins, low albedo Once melting begins, low albedo seawater replaces high albedo ice.seawater replaces high albedo ice.

• Greenhouse atmosphere helps to Greenhouse atmosphere helps to drive surface temperatures to almost drive surface temperatures to almost 50 degrees Celcius50 degrees Celcius

• Resumed evaporation helps warm Resumed evaporation helps warm atmosphere.atmosphere.

• Torrential rain would scrub some of Torrential rain would scrub some of CO2 out of air in form of carbonic CO2 out of air in form of carbonic acidacid

• Chemical erosion products would Chemical erosion products would quickly build up in ocean water which quickly build up in ocean water which would lead to precipitationwould lead to precipitation– Oxygen would again mix with oceanOxygen would again mix with ocean– Force iron to precipitate out with debris Force iron to precipitate out with debris

once carried by sea ice and glaciers.once carried by sea ice and glaciers.

IsotopesIsotopesWhat is an isotope?What is an isotope?• An atom always has the same An atom always has the same

number of protons, or positively number of protons, or positively charged particles, but the number of charged particles, but the number of electrons and neutrons may differ. electrons and neutrons may differ. An isotope of an atom contains more An isotope of an atom contains more or fewer neutrons than the average. or fewer neutrons than the average. To see if an atom is an isotope, look To see if an atom is an isotope, look at the atomic mass. at the atomic mass.

IsotopesIsotopes

CarbonCarbon• Carbon supplied Carbon supplied

to the ocean and to the ocean and atmosphere atmosphere comes from comes from outgassing of outgassing of carbon dioxide by carbon dioxide by volcanoes, and volcanoes, and contains about contains about 1% carbon-13 and 1% carbon-13 and 99% carbon-12. 99% carbon-12.

But that’s not the whole story…

CarbonCarbon

• In the oceans, carbon is removed by In the oceans, carbon is removed by the burial of calcium carbonate. If the burial of calcium carbonate. If this were the only process in effect, this were the only process in effect, calcium carbonate would have the calcium carbonate would have the same ratio of carbon-13 and carbon-same ratio of carbon-13 and carbon-12 as the volcanic output. 12 as the volcanic output.

CarbonCarbon

• BUT, carbon is also removed from the BUT, carbon is also removed from the ocean in the form of organic matter, ocean in the form of organic matter, and organic carbon is depleted in and organic carbon is depleted in carbon-13 (2.5% less than in calcium carbon-13 (2.5% less than in calcium carbonate). Modern calcium carbonate). Modern calcium carbonate is enriched in carbon-13 by carbonate is enriched in carbon-13 by approximately 0.5% relative to the approximately 0.5% relative to the volcano source (Hoffman).volcano source (Hoffman).

CarbonCarbon• So, if there was less biological So, if there was less biological

productivity, would carbonate records productivity, would carbonate records show higher or lower carbon-13 values? show higher or lower carbon-13 values?

CarbonCarbon• According to According to

Hoffman and Hoffman and Schrag, “Even the Schrag, “Even the meteorite impact meteorite impact that killed off the that killed off the dinosaurs 65 dinosaurs 65 million years ago million years ago did not bring did not bring about such a about such a prolonged collapse prolonged collapse in activity.”in activity.”

OrganismsOrganisms

The Neoproterozoic “Freeze-Fry”The Neoproterozoic “Freeze-Fry”

• What implication does this have for What implication does this have for the evolution of life?the evolution of life?

• Could organisms have survived?Could organisms have survived?

ExtremophilesExtremophilesExtremophiles are organisms that live Extremophiles are organisms that live

in extreme conditions. Evidence for in extreme conditions. Evidence for survival of these organisms during survival of these organisms during snowball earth events are found in snowball earth events are found in

these areas:these areas:• Hydrothermal vent communitiesHydrothermal vent communities• Hot springsHot springs• Very cold areas - cold-loving Very cold areas - cold-loving

organisms (psychrophilic)organisms (psychrophilic)

ExtremophilesExtremophiles

Evolution of LifeEvolution of LifeCould the freeze-fry events have Could the freeze-fry events have

actually encouraged evolution?actually encouraged evolution?

Bottleneck EffectBottleneck Effect

• Population bottleneck and flushes Population bottleneck and flushes (environmental filters) are (environmental filters) are observed to accelerate evolution in observed to accelerate evolution in some species (Hoffman). some species (Hoffman).

• It is known that various organisms It is known that various organisms undergo chromosomal undergo chromosomal reorganization in the face of reorganization in the face of environmental crisis (Carson). environmental crisis (Carson).

Post-Snowball Post-Snowball EnvironmentEnvironment• Snowball seawater was laden with Snowball seawater was laden with

nutrients due to hydrothermal activity nutrients due to hydrothermal activity and limited organic productivity. and limited organic productivity.

• Once the snowball oceans began to Once the snowball oceans began to melt, productivity and burial of organic melt, productivity and burial of organic matter increased, and oxygen was matter increased, and oxygen was released to the atmosphere. released to the atmosphere.

• This rise in free oxygen could be the This rise in free oxygen could be the cause of the explosion of life after the cause of the explosion of life after the snowball events.snowball events.

Emergence of AnimalsEmergence of Animals

Arguments AgainstArguments AgainstObliquity/SeasonalityObliquity/Seasonality::• A high obliquity (greater than 54A high obliquity (greater than 54) )

would allow the poles to receive more would allow the poles to receive more energy than the equator, and ice energy than the equator, and ice could form at the equatorcould form at the equator

• But high obliquity enhances But high obliquity enhances seasonality. Stronger seasonality seasonality. Stronger seasonality increases summer ablation and also increases summer ablation and also decreases accumulation of winter decreases accumulation of winter snow because colder air tends to be snow because colder air tends to be drier. drier.

Obliquity/SeasonalityObliquity/Seasonality

Arguments AgainstArguments AgainstInertial-Interchange True Polar Inertial-Interchange True Polar

Wander:Wander:• Entire crust and mantle rotates Entire crust and mantle rotates

relative to Earth’s spin axisrelative to Earth’s spin axis • Rapid transitions from low-latitude Rapid transitions from low-latitude

to high latitudeto high latitude • Explains how equatorial glaciation Explains how equatorial glaciation

could have occurred without a deep could have occurred without a deep freezefreeze

Arguments AgainstArguments AgainstEvidence for open ocean at equatorEvidence for open ocean at equator::• SimulationsSimulations found that an area of open found that an area of open

water in the equatorial oceans is water in the equatorial oceans is consistent with the evidence for consistent with the evidence for equatorial glaciation at sea levelequatorial glaciation at sea level

• In a more complex model, Earth was In a more complex model, Earth was able to freeze over in a slab ocean, but able to freeze over in a slab ocean, but in the real ocean model, it transports in the real ocean model, it transports enough heat in currents to the ice enough heat in currents to the ice margin to hold the ice off (Kerr). margin to hold the ice off (Kerr).

Varanger simulation which combines reduced Varanger simulation which combines reduced solar luminosity, 40 ppm of CO2, and reduced solar luminosity, 40 ppm of CO2, and reduced ocean heat transport. The simulation runs 60 ocean heat transport. The simulation runs 60

model years from initial, non-snowball model years from initial, non-snowball conditions until an equilibrium result is conditions until an equilibrium result is

obtained.obtained.

Arguments AgainstArguments Against

Survival of life without Survival of life without sunlight/oxygensunlight/oxygen::

• organic photosynthesis would be organic photosynthesis would be severely reduced for millions of severely reduced for millions of years because ice cover would block years because ice cover would block out sunlight out sunlight

• Meltwater poolsMeltwater pools• Bare groundBare ground

Arguments AgainstArguments Against• StrontiumStrontium::• 8787Sr/Sr/8686Sr should decline during snowball Sr should decline during snowball

events due to hydrothermal dominance events due to hydrothermal dominance and decreased riverine input and organic and decreased riverine input and organic productivityproductivity

• 8787Sr/Sr/8686Sr is sensitive to buffering by Sr is sensitive to buffering by carbonate dissolution and has a long carbonate dissolution and has a long residence timeresidence time

• Evidence has found that glacial and post-Evidence has found that glacial and post-glacial glacial 8787Sr/Sr/8686Sr ratios were not significantly Sr ratios were not significantly different from preglacial values (Hoffman).different from preglacial values (Hoffman).

Future Snowball Earth?Future Snowball Earth?

• Coldest state since the Coldest state since the NeoproteroziocNeoproterozioc for the last millions for the last millions yearsyears

• Approximately 80,000 years from Approximately 80,000 years from the next glacial maximumthe next glacial maximum

• Evidence suggests that the last Evidence suggests that the last several cycles have been getting several cycles have been getting stronger and stronger (Hoffman)stronger and stronger (Hoffman)

Future Snowball Earth?Future Snowball Earth?

• During the last glacial maximum During the last glacial maximum (20,000 years ago), the deep (20,000 years ago), the deep ocean cooled to near its freezing ocean cooled to near its freezing points, and sea ice reached points, and sea ice reached latitudes as low as 40latitudes as low as 40 to 45 to 45 North North

• Could the next ice age reach the Could the next ice age reach the critical latitude? critical latitude?

Snowball Earth

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