Topic 5: Snowball Earth

first supercontinent

Rodinia, formed around 1.2 Gyr, persisted for nearly 450mil years

Wilson Cycle

The cyclical opening and closing of ocean basins caused by movement of the Earth's plates.

Sturtian Glaciation

715-680 Myr ago, first phase of ice advance during mid-Neoproterozoic Snowball Earth episode

Marionan Glaciation

650-632 Myr, second ice advance

cause of first major glaciation

breaking up of Rodinia, preponderance of land masses

how does chemical weathering reduce global temp

increased rainfall taking CO2 out of the air, speeding up erosion and weathering of continental rocks, reducing atmospheric CO2

white ice

high albedo, reflects more solar energy - about 92% of incoming sunlight is reflected away. creates positive feedback which continues to reduce global temp

what induced melting of snowball earth

volcanoes releasing CO2 into atmosphere and ocean, increasing surface temp. sea ice near equator melted first, leading to positive feedback causing more melting and a decrease in albedo

tillites

Ancient glacial deposits preserved within a rock sequence

cap carbonates

Huge, thick carbonate rock over layers of glacial deposits, show temp conditions abruptly switched from glacial to tropical

tubestone stromatolite

sedimentary structure in cap carbonates, fossilized microbial mats. very thin, grow in tight proximity

aragonite fans

crystal, blade-like, CaCO3. grew perpendicular to ancient seafloor. large size suggests rapid crystallization of carbonate allowing huge crystals to grow upward

glaciation impacts on biosphere

marked decline in microbial and macrofauna diversity

polynya

pockets of open water near coast where some species may have found refuge

how did bacteria survive glaciation?

in layers of dirty ice (cryoconite) covering shallow seas. darkening of the ice absorbs solar radiation, melting snow/ice beneath the debris deposit

metazoan embryos

oldest physical evidence of animals, 630 million years ago. fossil eggs and embryos preserved at early stage of development

Ediacaran fauna

soft-bodied marine animals, fossils dating to 575 Myr. went extinct during Cambrian explosion