Sunday, January 17, 2016

Geosonnet 36

When sand dunes, glac'ers spread across the farm
Migration to a sanctuary's best.
We need an Eden, Oregon lest harm
Befall environments which are distressed.
Six hundred fifty million years ago
The glac'ers covered every continent
Yet benthic evolution did not slow.
How'd life the frozen ocean circumvent?
A diamictite sandwich of black shale
With fossil seaweed as the veg'table.
In open water haven, they prevail
Suggesting snowball Earth was just a fable.
   This promised land of cryogenic times.
   Requires small, locally mild climes.

Geology 43 507

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Chris Phoenix said...

Snowball Earth pre-dates the Cambrian. Surely animal and bacterial life could have survived just fine around hydrothermal vents, even under ice?

Obviously, oxygen-fixing organisms existed both before and after the alleged snowball, and presumably would have needed sunlight. But algae can live on glaciers. There wouldn't have been dust to provide minerals, but there would have been volcanoes.

This paper presents evidence of multicellular algae-type plants in the middle of the glaciation. I don't see a major problem with a lineage going back and forth from multicellular to single-celled as conditions required.

So why is Snowball Earth thought to be such a barrier to life?

C W Magee said...

The point is that the fossils show the continual evolution of large photosynthetic organisms, which are assumed to have lived somewhere close to the surface in open water. Can you get the full text, or are you stuck with abstract only?

Chris Phoenix said...

I'm stuck with abstract only.

If the fossils are detailed enough to show continual evolution of large photosynthetic organisms, then I retract my point. If they just show scattered points in a continuous lineage, then it seems plausible that a single lineage could go large, evolve for a while, leave fossils, go single-celled as conditions required, then go multi-celled again when the water opened up... lather, rinse, repeat.

C W Magee said...

Beautiful pictures of previously-Ediaacaran-to-Cambrian fossils from the Cryogenian. As well as continuous older forms.