Snowball Earth Flashcards
What was earth like after the last snowball?
1% oxygen, mostly slimy life, multicellular algae.
How many snowballs were there? Names?
3!
Huronian 2.2Ga, right before proterozoic Sturtian 700Ma, separating phanerozoic Marinoan 640Ma.
The two together are called Cryogenian. (neoproterozoic)
Rose global o2 to 1%, and eukaryotes developed (multicellular algae)
What is some evidence for the snowball earth?
Whats an issue with this theory?
Brian Hardland (1940s) shows glacial sedimentary deposits and landforms called DROPSTONES: large cobble boulders on sedimentary layers that were ‘dropped’ from glaciers onto body of water as the glacier hit water (release rocks that were picked up along the way).
left by glaciation.
proxy for glacial activity
600Ma on every continent.
Shows glacial episode from pole to equator.
PROBLEM: how would you know dropstones were actually formed at the equator and didn’t just move there later. - plate tectonics
What is the problem with snowball earth hypothesis and modeling of climatic effects?
If the earth’s temperature dropped that much, it would be a positive feedback loop once it hit texas and would never leave that temp again!
(proposed by Bikhail Budyko)
More sunlight reflected than absorbed. Pos feedback
Who was Joe Kirschvink?
Scientist who investigated paleomagnetism at dropstone locations from Neoproterozoic (Cyrogenian).
Paleomagnetism: see fossilized magnets.
Basalt has iron minerals, when lava erups, minerals move around and as they slow they lock into a magnetic position towards the pole with a specific angle in respect to surface of the planet. (near equator they are parallel)
If you find locked in magnetism, that block of land can help determine paleo-latitude (not lontidude) by using a dipmeter
FOUND THAT IT HAD HAPPENED AT EQUATOR!!
HOW…????
How did snowballs start (in the cryogenian)? Series of events…
Breakup of Rodina in 830 Ma (prior to pangea)
Continents groups at equator surrounded by ocean (narrow seas/inlets) causing intense rain in the tropics.
Intense rain would cause silicate weathering.
Silicate weathering is carbonic acid dissolving rocks.
Carbonic acid is co2 in water.
The acid attacks rocks that create clays and clays are deposited as sediments. THis is drawing C02 down from the atmosphere.
Flood basalt had just occured in artic canada. Basalt weathers and draws down C02 (susceptible to silicate weathering)
When c02 reaches a low, ice creeps towards equator. When this hits texas, positive feedback creates super thick global ice (according to Budyko). Albedo reflects more than is absorbed.
How do we get OUT of snowball events??
Plate tectonics would continue, so VOLCANISM. It would melt the ice a little, but would mostly release CO2 gas which would build up, over 10m years.
Since there was no silicate weathering, no C02 drawdown, the buildup would be like 10% co2 in the atmosphere. reflectivity overpowered by greenhouse and there would be a massive temp change (-50-50 over 2000 yers) ULTRAGREENHOUSE EFFECT
what is the evidence to the sudden end of a snowball earth?
Paul Hoffman in Namibia found glacial deposits (dropstones) followed by CAP CARBONATES (only found in warm contitions): limestone or dolostone) without any unconformities!!
suggesting rapid environmental change
Where do cap carbonates come from?
Warm water following the snowball, leads to high evaporation from oceans, the first clouds in a long time!!
Causes HYPER HURRICANES which mixes everything around, washing excess c02 out of the atmosphere, causing intense silicate weathering on land, the calcium and carbonate ions produced are washed into oceans and precipitate as cap carbonates
What are the phases/ cycle of snowball earth?
1: earth cools, ice advances towards equator
2. ice hits texas causing positive feedback, snowball forms
3. co2 builds up in atmosphere until it gets critial, ultra greenhouse effect, ice melts. c02 from volcanos, nothing to draw it down
4. hot aftermath, hyperhurricanes, deposition of cap carbonates
normal conditions again!
What is the paradox of phototrophs?
How would photosynthetic organisms survive ice if sunlight couldn’t penetrate??
3 solutions
1) slushball earth
2) hoffman’s suggestion of cracks in ice. tension creates cracks for sunlight penetration. Tension gashes.
3) subglacial lakes in antarctic very slowly cooled making it pure and allowing some sunlight to penetrate in thin areas. Blue light allowing for microbial and photosynthetic life.
What would hyperhurricanes do?
Mix the oceans!
Along with silicate weathering, the oceans would be flooded with nutrients for photosyntheitc life, aka a pulse of oxygen and greenery!
What is the consequence of higher levels of oxygen?
- larger creatures (diffusion of oxygen)
- end of sulfidic oceans (more o2 in oceans, less hydrogen sulfide gas, unrestricted availability of key metals for complex metabolisms)
- collagen (fibrous protein structural framework for large organisms. formed in oxic conditions! only able to do so after final marinoan snowbal
- Ozone: formed from o3, splitting of o2 by ultravoilet radiation, protecting the world from UV rays allows for exitance without radiation issues.
What would ozone layers allow for?
Opens up shallow environment for living and more creatures (makes it habitable and not crazy uv penetration) - used to be dangerous to metozoans but now its chill!
What is bioturbation?
Interaction with the environment. Releasing chemicals into water column, life burrowing in sediments, larger creatures evolving as 02 levels rise.
