Snowball earth

What is snowball earth? and how many were there?

Late proterozoic global glaciation

2, maybe 3 global glaciations- Sturtian glaciation (715 Mya - 680 Mya), Marinoan (650 mya- 635 mya), and Gaskiers (580mya)

What caused Snowball earth?

a positive feedback of cooling across the world

• After Rondinia broke up, many small continents were scattered around the equator → lots of surface area= lots of area for chemical weathering -→ removes a lot of CO2 from atmosphere → temp decreases

• Albedo effect: temperature falling increases Ice at poles → ice reflects more light, preventing warming → temp falls further, cycle repeats

Why are snowball events relatively short lived (geologically speaking)?

Volcanos continue to pump out CO2, which would warm the atmosphere since it could not be weathered and absorbed by the glaciation

How do you get into a snowball earth cycle?

After a snowball earth melts, you are left with a hothouse earth, which reveals areas where the glacier scrapped off the top layer of rock and exposed unweathered rock- carbon then starts to get drawn down into weathering again, starting the ice feedback loop all over again

What is some evidence for snowball earth?

• Glacial features such as tillites (deposits of poorly sorted sediment)

• Rapid deposition of carbonate rocks directly on top of glacial debris- suggests that they were deposited during a period where sea levels rose rapidly

• tubestone stromatolites- indicate that water was precipitating so much carbonate that only the faster growing stromatolites avoided being covered

• aragonite fans

• resurgence of banded iron formations- oceans were not oxygenated during glaciation, so iron built up and oxidized once ice melted and oceans reoxygenated

How did life survive these snowballs?

Refugias

• pockets of open water where ice was blown offshore

• in pelagic waters of a circum-equatorial ocean

• around shallow hot springs associated with volcanic islands

• next to black smokers underwater

• layers of dirty ice (layer of small rock particles, soot, and bacteria)

perhaps also under the ice, photosynthesis can occur under 100 meters of ice (ice was only about 10 meters thick)

How did snowball earth help animals come into existence?

Hypothetically- the glacier melt into the ocean contained more phosphate, allowing more cyanobacteria to bloom, increasing oxygen levels in the world

What is the oldest physical evidence of animals?

630 million year old egg and embryo fossils (found in china)

What are Edicarian fauna?

a diverse group of soft-bodied marine animals that evolved after the last snowball earth (620 mya), but went extinct during the cambrian explosion, leaving body fossils and some trace fossils