Dodging Snowballs: Geochronology of the Gaskiers glaciation and the first appearance of the Ediacaran biota

Dodging snowballs: Geochronology of the Gaskiers glaciation and the first appearance of the Ediacaran biota
Judy P. Pu; Samuel A. Bowring; Jahandar Ramezani; Paul Myrow; Timothy D. Raub; Ed Landing; Andrea Mills; Eben Hodgin; Francis A. Macdonald
Geology (2016) 44 (11): 955–958.
https://doi.org/10.1130/G38284.1

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This is a short, sweet, four page paper. It has a 32-item, three-quarter page bibliography that looks to be chock-full of snowball earth refereed, pre-LLM, papers.

As I read it, this paper contains two main contributions:

  1. Putting a 340K-1.51M year time span on the Gaskiers glaciation, too short to make that glaciation a “snowball earth” period.
  2. Dating the Mistaken Point fossils more accurately, to 570.94 &plusminus; 0.38 Ma.

Apparently there is some paleomagnetic data that puts the rocks that are studied in this paper at a low latitude, so it’s weird that glaciation shows up without a snowball earth.

There’s a few consequences to these findings.

  1. “Gaskiers glaciation may not have been a critical barrier for macroscopic animal evolution.”
  2. “Gaskiers glaciation represents a metastable state with significant open water, or that a snowball earth event was ended by other than CO2 buildup.”

They can neither confirm nor deny a snowball earth during the Gaskiers glaciation, and they cast a little doubt on snowball earth theories in general.

These authors wrestle with the oxygen control hypothesis a little:

…the fortuitous preservation of the fossils below volcanic tuff layers suggests a taphonomic control, and morphologically complex animals may have been present before the Gaskiers glaciation without necessarily being limited by oxygen availability.

I interpret “taphonomic control” to mean that some physical property of the world prevented fossilizing early Ediacaran animals. It’s lucky that the volcanic tuff layers sandwiched the Newfoundland Edicaran animals in sandstone layers, leading to preservation.