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SUMMARY:Ecosystem Relocation on Snowball Earth: polar-alpine ancestry of t
 he modern surface biosphere - Paul Hoffman - University of Victoria (BC) a
 nd Harvard University
DTSTART:20231023T170000Z
DTEND:20231023T180000Z
UID:TALK207295@talks.cam.ac.uk
CONTACT:Lucas Measures
DESCRIPTION:There is now compelling evidence that the world ocean was perp
 etually dark under global ice-shelves for 55 million years (Sturtian glaci
 ation) at the start of the Cryogenian Period (717−635 Ma) and again for 
 5−15 million years (Marinoan glaciation) at the end of that Period. Supp
 orting evidence comes from paleomagnetism\, geochronology\, sedimentology\
 , geochemistry and numerical simulations of atmosphere−ice−ocean dynam
 ics. The latter suggest that the time lapse from an ice-albedo tipping poi
 nt at 35% ocean area ice-covered to total darkness was ≤400 years. Yet\,
  there is undeniable fossil evidence for marine phytoplankton including eu
 karyotic algae before\, between and soon after the Cryogenian panglacial c
 hrons. This talk will pose and test the hypothesis that polar−alpine mic
 robial ecosystems\, established long before the Cryogenian\, simply moved 
 with their ice margins to the equatorial zone of net ablation on Snowball 
 Earth\, where their habitat area was vastly enlarged and the cruelty of wi
 nter reduced. They thrived and evolved\, and when each Snowball chron ende
 d\, some returned to the mountaintops while others inhabited a rapidly-war
 ming\, meltwater-dominated\, nutrient-rich and biologically vacant surface
  ocean. Accordingly\, the extant surface biosphere is derived from a parti
 cular subset of pre-Cryogenian life. It will be argued from modern analogs
  that Tonian polar−alpine habitats had sufficient ecologic\, taxonomic a
 nd genomic diversity to account for the observed post-Cryogenian biotic ra
 diations. Polar−alpine ancestry and Snowball equatorial intermediaries r
 ationalize otherwise problematic aspects of the molecular phylogenomics of
  many living marine and terrestrial organisms.
LOCATION: Harker 1\, Department of Earth Sciences\, Downing Street
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