Driver of the largest mass extinction in the history of the Earth
identified
New study provides a comprehensive reconstruction of the Permian-Triassic boundary event

Date:
October 19, 2020
Source:
Helmholtz Centre for Ocean Research Kiel (GEOMAR)
Summary:
252 million years ago, at the transition from the Permian to the
Triassic epoch, most of the life forms existing on Earth became
extinct. Using latest analytical methods and detailed model
calculations, scientists have now succeeded for the first time to
provide a conclusive reconstruction of the geochemical processes
that led to this unprecedented biotic crisis.



FULL STORY ==========================================================================
Life on Earth has a long, but also an extremely turbulent history. On
more than one occasion, the majority of all species became extinct and
an already highly developed biodiversity shrank to a minimum again,
changing the course of evolution each time. The most extensive mass
extinction took place about 252 million years ago. It marked the end of
the Permian Epoch and the beginning of the Triassic Epoch. About three
quarters of all land life and about 95 percent of life in the ocean
disappeared within a few thousands of years only.


========================================================================== Gigantic volcanic activities in today's Siberia and the release of
large amounts of methane from the sea floor have been long debated
as potential triggers of the Permian-Triassic extinction. But the
exact cause and the sequence of events that led to the mass extinction
remained highly controversial. Now, scientists from Germany, Italy and
Canada, in the framework of the EU-funded project BASE-LiNE Earth led by
Prof. Dr. Anton Eisenhauer from GEOMAR Helmholtz Centre for Ocean Research
Kiel in cooperation with the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, have for the first time been able to conclusively reconstruct the entire cascade of events at that time using cutting-edge analytical techniques and innovative geochemical modelling. The study
has been published today in the international journal Nature Geoscience.

For their study, the BASE-LiNE Earth team used a previously often
neglected environmental archive: the shells of fossil brachiopods. "These
are clam-like organisms that have existed on Earth for more than 500
million years. We were able to use well-preserved brachiopod fossils
from the Southern Alps for our analyses. These shells were deposited
at the bottom of the shallow shelf seas of the Tethys Ocean 252 million
years ago and recorded the environmental conditions shortly before and
at the beginning of extinction," explains Dr.

Hana Jurikova. She is first author of the study, which she conducted as
part of the BASE-LiNE Earth project and her doctoral thesis at GEOMAR.

By measuring different isotopes of the element boron in the fossil shells,
the team was able to trace the development of the pH values in the ocean
252 million years ago. Since seawater pH is tightly coupled to the CO2 concentration in the atmosphere, the reconstruction of the latter was also possible. For the analyses, the team used high-precision isotope analyses
at GEOMAR as well as high-resolution microanalyses on the state-of-the-art large- geometry secondary ion mass spectrometer (SIMS) at GFZ.

"With this technique, we can not only reconstruct the evolution of the atmospheric CO2 concentrations, but also clearly trace it back to volcanic activity. The dissolution of methane hydrates, which had been suggested
as a potential further cause, is highly unlikely based on our data,"
explains Dr.

Marcus Gutjahr from GEOMAR, co-author of the study.

As a next step, the team fed their data from the boron and additional
carbon isotope-based investigations into a computer-based geochemical
model that simulated the Earth's processes at that time. Results
showed that warming and ocean acidification associated with the immense volcanic CO2 injection to the atmosphere was already fatal and led to
the extinction of marine calcifying organisms right at the onset of the extinction. However, the CO2 release also brought further consequences;
with increased global temperatures caused by the greenhouse effect,
chemical weathering on land also increased.

Over thousands of years, increasing amounts of nutrients reached the
oceans via rivers and coasts, which then became over-fertilized. The
result was a large- scale oxygen depletion and the alteration of entire elemental cycles. "This domino-like collapse of the inter-connected life-sustaining cycles and processes ultimately led to the observed catastrophic extent of mass extinction at the Permian-Triassic boundary," summarizes Dr. Jurikova.

The study was conducted within the framework of the EU-funded ITN project
BASE- LiNE Earth, in which the use of brachiopods as an environmental
archive was systematically studied for the first time, and relevant
analytical methods were improved and newly developed. "Without these new techniques it would be difficult to reconstruct environmental processes
more than 250 million years ago in the same level of detail as we have
done now," emphasizes Prof. Dr.

Anton Eisenhauer from GEOMAR, the former BASE-LiNE Earth project
coordinator and co-author of the new study, "in addition, the new methods
can be applied for other scientific applications."

========================================================================== Story Source: Materials provided by Helmholtz_Centre_for_Ocean_Research_Kiel_(GEOMAR). Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Hana Jurikova, Marcus Gutjahr, Klaus Wallmann, Sascha Flo"gel,
Volker
Liebetrau, Renato Posenato, Lucia Angiolini, Claudio Garbelli, Uwe
Brand, Michael Wiedenbeck, Anton Eisenhauer. Permian-Triassic
mass extinction pulses driven by major marine carbon
cycle perturbations. Nature Geoscience, 2020; DOI:
10.1038/s41561-020-00646-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201019125512.htm

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