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Methanogen archaea in end-Permian extinction (free pdf) + Triassic-Jurassic fossil record sampling



From: Ben Creisler
bcreisler@gmail.com

New papers that may be of interest:

In open access:

Daniel H. Rothman, Gregory P. Fournier, Katherine L. French, Eric J.
Alm, Edward A. Boyle, Changqun Cao, and Roger E. Summons (2014)
Methanogenic burst in the end-Permian carbon cycle.
Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1318106111
http://www.pnas.org/content/early/2014/03/26/1318106111.abstract?sid=8486237f-a59e-4541-b635-a060b08f52cb



Significance

The end-Permian extinction is the most severe biotic crisis in the
fossil record. Its occurrence has been attributed to increased CO2
levels deriving from massive Siberian volcanism. However, such
arguments have been difficult to justify quantitatively. We propose
that the disruption of the carbon cycle resulted from the emergence of
a new microbial metabolic pathway that enabled efficient conversion of
marine organic carbon to methane. The methanogenic expansion was
catalyzed by nickel associated with the volcanic event. We support
this hypothesis with an analysis of carbon isotopic changes leading up
to the extinction, phylogenetic analysis of methanogenic archaea, and
measurements of nickel concentrations in South China sediments. Our
results highlight the sensitivity of the Earth system to microbial
evolution.

Abstract

The end-Permian extinction is associated with a mysterious disruption
to Earth's carbon cycle. Here we identify causal mechanisms via three
observations. First, we show that geochemical signals indicate
superexponential growth of the marine inorganic carbon reservoir,
coincident with the extinction and consistent with the expansion of a
new microbial metabolic pathway. Second, we show that the efficient
acetoclastic pathway in Methanosarcina emerged at a time statistically
indistinguishable from the extinction. Finally, we show that nickel
concentrations in South China sediments increased sharply at the
extinction, probably as a consequence of massive Siberian volcanism,
enabling a methanogenic expansion by removal of nickel limitation.
Collectively, these results are consistent with the instigation of
Earth's greatest mass extinction by a specific microbial innovation.


Stories:

http://phys.org/news/2014-03-methane-producing-microbes-responsible-largest-mass.html

http://www.nature.com/news/archaeageddon-how-gas-belching-microbes-could-have-caused-mass-extinction-1.14958

===

Alexander M. Dunhill, Michael J. Benton, Richard J. Twitchett & Andrew
J. Newell (2014)
Testing the fossil record: sampling proxies and scaling in the British
Triassic-Jurassic.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
http://dx.doi.org/10.1016/j.palaeo.2014.03.026
http://www.sciencedirect.com/science/article/pii/S0031018214001527

The quality of the fossil record varies immensely across taxa,
geographic regions, environments and time intervals. Because much of
this variation can be confounded when examining global patterns, we
present a detailed investigation of the British Triassic and Jurassic,
one of the most intensively studied pairs of systems in the world.
Marine Jurassic palaeodiversity is at least partly controlled by rock
availability and accessibility. The terrestrial record is patchier,
and effects of rock availability are overprinted by a stronger signal
of sporadic preservation. These results also fit a sea-level driven
common-cause explanation, as one would expect to see close correlation
between rock availability and palaeodiversity in the marine realm, but
less so in the terrestrial. Formation counts and palaeodiversity do
not correlate, a surprising result given the number of earlier studies
that have found close correlations. However, this study differs from
most others in that formation counts and palaeodiversity metrics are
derived from independent data sources, and so within-study redundancy
is avoided. The study confirms the complexity of rock-fossil time
series, and the likelihood that the fossil record documents a complex
mix of potential biological signal, common cause signal, and rock
record and sampling bias. It may be impossible to identify a useful
simple sampling proxy for the fossil record that captures every bias
and sampling error. Ironically, when preservation is good, sampling
proxies representing rock availability, such as outcrop area, can be
used to predict palaeodiversity, but are ineffectual when the fossil
record is patchy.

Highlights

The British Triassic and Jurassic provide rich resources on rock and
fossil records
Marine and terrestrial diversity data interact differently with sampling proxies
Sampling proxies predict diversity in the marine, but not in the
terrestrial data
Sampling proxies are only useful when preservation is consistent (i.e. marine)
Distinguishing 'real' from biased diversity signals may be impossible