Bacterial bloom as the Earth thawed: Photosynthetic organisms during the Snowball Earth

Date:
August 27, 2021
Source:
Tohoku University
Summary:
Around 650 million years ago, the Earth entered into the Marinoan
glaciation that saw the entire planet freeze. The 'Snowball Earth'
impeded the evolution of life. But as it warmed, biotic life began
to flourish. A research team has now analyzed rock samples from
China to tell us more about this transition.



FULL STORY ==========================================================================
Some researchers hypothesize that ice sheets enveloped the earth during
the Marinoan glaciation (650-535 million years ago) in what is dubbed the "Snowball Earth." The glaciation also impacted the climate and chemical compositions of the oceans, restraining the evolution of early life. Yet,
as the earth warmed, and the Ediacaran period dawned, biotic life began
to evolve.


==========================================================================
A research team from Tohoku University has unveiled more about the
evolutionary process of the Marinoan-Ediacaran transition. Using
biomarker evidence, they revealed possible photosynthetic activity
during the Marinoan glaciation. This was followed by photosynthetic
organisms and bacteria entering a period of low productivity. However,
as eukaryotes expanded during the early Ediacaran period, they blossomed.

Dr. Kunio Kaiho, who co-authored a paper with Atena Shizuya, said, "Our findings help clarify the evolution of primitive to complex animals in
the aftermath of the Snowball Earth." Their paper online was published
in the journal Global and Planetary Change on August 8, 2021.

The late Neoproterozoic era (650-530 million years ago) witnessed
one of the most severe ice ages in the Earth's 4.6-billion-year
history. Researchers believe that ice sheets covered the entire
earth since glaciogenic units, such as ice-rafted debris, are
distributed globally. Overlaying these glaciogenic formations are
cap carbonates. These precipitate under warm conditions and therefore
suggest that the glacial environment changed rapidly into a greenhouse environment.

The Snowball Earth hypothesis purports the atmospheric carbon dioxide concentration controlled the change from a frozen state to an ice-free
state.

Ice sheet-covered oceans prevented the dissolution of carbon dioxide
into seawater during the Marinoan ice age, meaning greenhouse gas concentration, emitted by volcanic activity, increased gradually. Once
the extreme greenhouse effect kicked in, glaciers melted and excess
carbon dioxide precipitated on glaciogenic sediments as cap carbonates.

Whilst the Snowball Earth theory explains the wide distributions
of glacial formations, it fails to shed light on the survival of
living organisms. To counteract this, some researchers argue that
sedimentary organic molecules, a molecular clock, and fossils from the
late Neoproterozoic era are evidence that primitive eukaryotes such as
sponges survived this severe ice age. Alternative models also propose
that an ice-free open sea existed during the glaciation and acted as an
oasis for marine life.

But what is understood is that the Marinoan glaciation and the succeeding extreme climatic transition likely had a marked impact on the biosphere.

Shortly after the ice age, the Lantian biota, the earliest-known complex macroscopic multicellular eukaryotes, emerged. The Lantian biota includes macrofossils that are phylogenetically uncertain but morphologically and taxonomically diverse. Meanwhile, pre-Marinoan species have simple body
plans with limited taxonomic variety.

Bacteria and eukaryote biomarkers demonstrate that bacteria dominated
before the glaciation, whereas steranes/hopanes ratios illustrate that eukaryotes dominated just before it. However, the relationship between
the biosphere changes and the Marinoan glaciation is unclear.

In 2011, Kaiho and his team traveled to Three Gorges, China under
the guidance of China University of Science's Dr. Jinnan Tong to take sedimentary rock samples from the deeper outcrops of marine sedimentary
rocks. From 2015 onwards, Shizuya and Kaiho analyzed the biomarkers
of algae, photosynthetic activity, bacteria, and eukaryotes from the
rock samples.

They found photosynthetic activity based on n-C17 + n-C19 alkanes for
algae and pristane + phytane during the Marinoan glaciation. Hopanes
within the early and late carbonate deposition showed photosynthetic
organisms and other bacteria entering a state of low productivity
before recovering. And steranes from carbonates and mudstones after
the cap carbonate deposition from the early Ediacaran period indicated
the expansion of eukaryotes. The expansion of eukaryotes corresponded
to the Lantian biota being morphologically diverse when compared to pre-Marinoan species.

Kaiho believes we are one step closer to understanding the evolutionary
process that occurred before and after Snowball Earth. "The environmental stress of closed ocean environments for the atmosphere followed by high temperatures around 60DEGC may have produced more complex animals in
the aftermath." Their findings show that bacterial recovery preceded eukaryotes' domination.

Kaiho's team is doing further studies to clarify the relationship
between climate change and the biosphere in other locations. They are
also studying the relationship between atmospheric oxygen increases and
animal evolution from the late Cryogenian to early Cambrian (650 to 500
million years ago).

========================================================================== Story Source: Materials provided by Tohoku_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Atena Shizuya, Kunio Kaiho, Jinnan Tong. Marine biomass changes
during
and after the Neoproterozoic Marinoan global
glaciation. Global and Planetary Change, 2021; 205: 103610 DOI:
10.1016/j.gloplacha.2021.103610 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210827121450.htm

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