https://www.nature.com/articles/s41467-023-37172-x (open access)

Abstract:

During the Marinoan Ice Age (ca. 654–635 Ma), one of the ‘Snowball Earth’ events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event,
as evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedded with glacial diamictites of the late Cryogenian Nantuo Formation in South China. However, the environmental conditions that allowed these organisms
to thrive are poorly known. Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas
nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia for
eukaryotic organisms during the waning stage of the Marinoan Ice Age.

--- SoupGate-Win32 v1.05
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On Tue, 4 Apr 2023 12:38:32 -0700 (PDT), the following
appeared in talk.origins, posted by erik simpson
<eastside.erik@gmail.com>:

https://www.nature.com/articles/s41467-023-37172-x (open access)

Abstract:

During the Marinoan Ice Age (ca. 654–635?Ma), one of the ‘Snowball Earth’ events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event, as

evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedded with glacial diamictites of the late Cryogenian Nantuo Formation in South China. However, the environmental conditions that allowed these organisms to
thrive are poorly known. Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas
nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia

for eukaryotic organisms during the waning stage of the Marinoan Ice Age.

Interesting; thanks for the ref.

I seemed to recall another glaciation era around 400-450
Mya; this article is an overview, and there have been more
glaciations than most people, including myself, realized:

https://en.wikipedia.org/wiki/Timeline_of_glaciation

I find interesting the conjecture that the warming at the
end of the Marinoan Ice Age influenced, and possibly caused,
the Cambrian Explosion.

--

Bob C.

"The most exciting phrase to hear in science,
the one that heralds new discoveries, is not
'Eureka!' but 'That's funny...'"

- Isaac Asimov

--- SoupGate-Win32 v1.05
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On Tuesday, April 4, 2023 at 1:30:11 PM UTC-7, Bob Casanova wrote:

On Tue, 4 Apr 2023 12:38:32 -0700 (PDT), the following
appeared in talk.origins, posted by erik simpson
<eastsi...@gmail.com>:

https://www.nature.com/articles/s41467-023-37172-x (open access)

Abstract:

During the Marinoan Ice Age (ca. 654–635?Ma), one of the ‘Snowball Earth’ events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event,

as evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedded with glacial diamictites of the late Cryogenian Nantuo Formation in South China. However, the environmental conditions that allowed these organisms
to thrive are poorly known. Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas
nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia

for eukaryotic organisms during the waning stage of the Marinoan Ice Age.

Interesting; thanks for the ref.

I seemed to recall another glaciation era around 400-450
Mya; this article is an overview, and there have been more
glaciations than most people, including myself, realized:

https://en.wikipedia.org/wiki/Timeline_of_glaciation

I find interesting the conjecture that the warming at the
end of the Marinoan Ice Age influenced, and possibly caused,
the Cambrian Explosion.

--

Bob C.

"The most exciting phrase to hear in science,
the one that heralds new discoveries, is not
'Eureka!' but 'That's funny...'"

- Isaac Asimov

It certainly did influence it, although the "explosion" came a bit later. The cap carbonates (most fasmously the
Doushantuo formation) is generally regarded as marking the beginning of the Ediacaran (~630 Mya) while the
Cambrian is currently defined as 542 Mya. While many (most) of the earlier Ediacaran organisms remain of
uncertain phylogenetic affinity with paleozoic fauna, several have been fairly well-established as at least
metazoa, and one (Ikaria) even as bilaterian. Many of the latest Ediacaran fauna (the "small shellies") have
obvious connections to panarthropods, brachiopods and molluscs.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Tue, 4 Apr 2023 14:25:45 -0700 (PDT), the following
appeared in talk.origins, posted by erik simpson
<eastside.erik@gmail.com>:

On Tuesday, April 4, 2023 at 1:30:11?PM UTC-7, Bob Casanova wrote:

On Tue, 4 Apr 2023 12:38:32 -0700 (PDT), the following
appeared in talk.origins, posted by erik simpson
<eastsi...@gmail.com>:

https://www.nature.com/articles/s41467-023-37172-x (open access)

Abstract:

During the Marinoan Ice Age (ca. 654–635?Ma), one of the ‘Snowball Earth’ events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event, as

evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedded with glacial diamictites of the late Cryogenian Nantuo Formation in South China. However, the environmental conditions that allowed these organisms to
thrive are poorly known. Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas
nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing

refugia

for eukaryotic organisms during the waning stage of the Marinoan Ice Age. >> >

Interesting; thanks for the ref.

I seemed to recall another glaciation era around 400-450
Mya; this article is an overview, and there have been more
glaciations than most people, including myself, realized:

https://en.wikipedia.org/wiki/Timeline_of_glaciation

I find interesting the conjecture that the warming at the
end of the Marinoan Ice Age influenced, and possibly caused,
the Cambrian Explosion.

It certainly did influence it, although the "explosion" came a bit later. The cap carbonates (most fasmously the
Doushantuo formation) is generally regarded as marking the beginning of the Ediacaran (~630 Mya) while the
Cambrian is currently defined as 542 Mya. While many (most) of the earlier Ediacaran organisms remain of
uncertain phylogenetic affinity with paleozoic fauna, several have been fairly well-established as at least
metazoa, and one (Ikaria) even as bilaterian. Many of the latest Ediacaran fauna (the "small shellies") have
obvious connections to panarthropods, brachiopods and molluscs.

A-a-a-a-nd you've gone far beyond the meager knowledge of a
retired EE. But thanks. :-)

--

Bob C.

"The most exciting phrase to hear in science,
the one that heralds new discoveries, is not
'Eureka!' but 'That's funny...'"

- Isaac Asimov

--- SoupGate-Win32 v1.05
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