Snowball Earth Flashcards
Snowball earth cause - tilts in obliquity
Reference
Complete snowball improbable, why?
Why are there low latitudinal glacial deposits?
Issues with idea - 3 wobbles… compromise?
Williams et al, 1998#
Complete snowball improbable because would have killed all photosynthetic life
Low latitudinal glacial deposits as earth tilt from 23.5 to 54 degrees. current day equator is at poles. Process called obliquity oblateness. Result of continents being at poles, mass imbalance tilts earth.
3 wobbles required which is unlikely, maybe initial tilting caused by impact allowing formation of ice at low latitudes. Before normal climate resumed
What caused snowball earth methane Reference What was role of methane in Proterozoic? What produced methane? What caused methane to become less abundant? What effect did this have?
Pavlov, 2002
Methane maintained warm temperatures, less oxygen, more methane
Methane produced by bacteria, other bacteria unable to survive
Oxidation event at end of Proterozoic
Decrease in methane triggered snowball
Timing of snowball and gap between cycles
Reference
tectonic forcing link (3 examples)
What does O’s and Sr isotopes suggest about how climate cooled?
What do isotopes suggest caused post glacial hothouse?
What effect would more mafic material have on ocean?
Rooney, 2014
Rafting of rodinia, emplacement of large igneous province at low latitudes and onset of sturtian glasciation
Before glaciation showed increase in magic material, implies more magic material was being weatheredproviding more Ca to draw down CO2 cooling climate
Intense weathering on continent dfue to hot house
Increase in CA promotes anoxic bacteria in oceans
Snowball or slushball Reference What is required for complete freezing? How far did ice go in previous studies? How far is ice on new study unfixed? Why? Conclusion? Unreliable?
Poulsen, 2003
Runaway albedo from ice at low latitudes
Ice went as far as 30 degrees in previous studies
current study with ice unfixed it retreated to 45 degrees
This occurred as sea temps still above 0. This may be down to limited ocean circulation trapping water around equator
Cap carbonates and hot house earth - greenhouse or transgression
Reference
Two arguments?
Explain effect of mass greenhouse gas release
Explain alternate hypothesis, evidence, why misread?
Kennedy and Christie-Glick 2011
Mass influx of greenhouse gas (Hofmann et al, 1998) or series of major transgressions
Greenhouse effect possible as melting of ice released CO2 plus rapid weathering of mountains and also volcsnism.
Alternative is cap carbonates deposited by transgression, same as modern day reef deposits but lack of skeletons makes people look for something else
Snowball earth and multicellular organisms
Reference
Why did complex life start at end of snowball?
What impact did rapid environmental change have?
Nutrient supply?
What produced O2?
Issue?
Walker, 2003
Extreme cold/ice may have wiped out much of the single celled bacteria/algae freeing up resources and niches for new life to flourish, lush environment allowed mutants toil survive and pass on genes
multicellularity developed as easier to cope with changing environment with specialised cells,
Build up of nutrients during snowball earth
o2 produced by photosynthesising algae and bacteria
Issue is multicellular algae dated at 1.2Ga, perhaps algae and animals developed differently
Why snowball earth has not happened again
Reference
Snowball events occurred before what?
How would this affect CO2?
What effect did lack of calcite mineralisation have on CO2?
What effect did high calcium carbonate concentrations have on oceans?
Graham-Rowe, 2003
Development of calcite mineralisation
This would have been a more efficient CO2 sink
Without organisms trapping CO2 Earth’s weak carbon feedback systems were knocked out of whack causing snowball
High CaCO3 in oceans reduces oceans capacity to store CO2.
