Snowball Earth Flashcards
what time period was the snowball earth?
middle of neoproterozoic
formation of neoproterozoic began at what event?
-formation of first supercontinent, Rodinia, at 1.2 bya
Rodinia lasted for how long? and broke up when?
-450 million years
-750-630 mya
what are the phases of ice advance during snowball earth episode?
-Sturtian glaciation (715-680 mya)
-Marionan glaciation (650-632 mya)
-Gaskiers glacation (less global evidence)
why did global glaciations happen?
rodinia breaks up and landmasses was positioned in the middle and low latitudes
what is declination?
measures the angular deviation between true and magnetic north
what is inclination?
the direction of earth’s magnetic field lines
magnetic lines run N-S and vary in dip with latitude. Effect on rock?
-magnetic materials in rock tells us magnetic north direction & magnetic latitude which tells us where rock was when it was magnetized
polar wander curve (def.)
poles are stationary but continents wander w/ time; magnetized rocks on single continent appear to different pole positions
chemical weathering effect on glaciation
-breakup of rondinia = increase landmass near water = increase rainfall = decrease CO2 in air = increase erosion/weathering
-decrease CO2 = fall in global temp
effect of ice albedo on glaciation
-ice has high albedo = reflects solar energy back into space
-reduce global temp
point of no-return for glacation
33 latitude north and south = cooling effect unstoppable -> equator froze over in a decade
global temp at this point
-50C
why are snowball earth short-lived?
volcanoes continued to release CO2 into atmosphere/ocean -> no weathering –> melting -> equator melting first (positive feedback)
evidence of snowball earth
-glacial deposits (tillites/dropstones)
-cap carbonate
-banded iron formation
how cap carbonate is formed?
-due to transient but intense greenhouse climate, rising sea levels
- increase weathering = increase alkalinity = increase carbonate precipitation on glacial debris
cap carbonate indicates what about the environment at the time?
conditions changed from glacial to tropical quickly; ocean was oversaturation with carbonate despite ocean acidification
what are tubestone stromatolite?
structure in cap carbonate; very thin and grow close together; growed in shallow water; indicated that water was precipitating carbonate quickly
what are aragonite fans?
feature in cap carbonate; blade in CaCO3 = grow perpendicular to seafloor
small BIF resurgence after snowball earth. why?
freezing of oceans = water stagnation = buildup of dissolved iron
ice melted. = ocean circulation starts = iron oxidized = BIF in oxic zones
consequence of snowball earth on biosphere
-decline in microbial/macrofauna diversity
place biosphere survived in snowball earth
-volcanic hot spring
-polynya = pockets of open H20 near coast
-under iceccaps ( photosynthesis happens hundreds of meters under ice, equator ice. = 10 m)
-cryoconite - dirty ice
-black smoker environments
why does cyanobacteria blooms after glaciers melt?
outwash has phosphate, increase cyanobacteria = increase oxygen
ediacaran fauna (def.)
appear in neoprote., bottom waters become oxic, sot-bodied marine animals
fossil lagerstatten (def.)
lots of fossils
other evidence of animals after glacitation
-shell bearing organisims (Cloudina)
-trace fossils
-burrowing
