Plants Kick-Started Evolutionary Drama of Earth's Oxygenation
ScienceDaily (Oct. 8, 2010) — An international team of scientists, exploiting pioneering techniques at Arizona State University, has taken a significant step toward unlocking the secrets of oxygenation of the Earth's oceans and atmosphere.
A panser shark (predatory fish greater than 30 feet long) is a consequence of the Earth's oxygenation event of 400 million years ago. (Credit: Staffan Waerndt / Swedish Museum of Natural History)
Evolution of the Earth's multitude of organisms is intimately linked to the rise of oxygen in the oceans and atmosphere. The new research indicates that the appearance of large predatory fish as well as vascular plants approximately 400 million years ago coincided with an increase in oxygen, to levels comparable to those we experience today. If so, then animals from before that time appeared and evolved under markedly lower oxygen conditions than previously thought.
The researchers, including collaborators from Harvard, Denmark, Sweden and the United Kingdom, made use of a method developed at ASU by Ariel Anbar, a professor in the department of chemistry and biochemistry and the School of Earth and Space Exploration in the College of Liberal Arts and Sciences, and his research group. The method can be used to estimate global oxygen levels in ancient oceans from the chemical composition of ancient seafloor sediments.
Their important findings are presented in a paper published in the Proceedings of the National Academy of Sciences (PNAS), titled "Devonian rise in atmospheric oxygen correlated to radiations of terrestrial plants and large predatory fish."
"There has been a lot of speculation over the years about whether or not oxygen in the atmosphere was steady or variable over the last 500 million years," explained Anbar, who leads ASU's Astrobiology Program. "This is the era during which animals and land plants emerged and flourished. So it's a profound question in understanding the history of life. These new findings not only suggest that oxygen levels varied, but also that the variation had direct consequences for the evolution of complex life."
The Earth is 4,500 million years old. Microbial life has probably thrived in the oceans for most of that time. However, until about 2,300 million years ago, the atmosphere contained only traces of oxygen. During that time, some microbes in the oceans likely produced oxygen as a byproduct of photosynthesis. But the quantities they produced were insufficient to accumulate much in the atmosphere and oceans. The situation changed with the "Great Oxidation Event," 2,300 million years ago. Oxygen levels rose again around 550 million years ago. The first animals appear in the fossil record at this time, marking the beginning of an era that geologists call the "Phanerozoic" -- a Greek word meaning "evident animals." This new work explores how oxygen levels changed during the Phanerozoic.
...
Read more here/Leia mais aqui: Science Daily
+++++
Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish
Tais W. Dahl a,b,1, Emma U. Hammarlund b,c,d, Ariel D. Anbar e,f, David P. G. Bond g, Benjamin C. Gill h, Gwyneth W. Gordon e, Andrew H. Knoll a,h, Arne T. Nielsen i, Niels H. Schovsbo j, and Donald E. Canfield b
+Author Affiliations
aDepartment of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138;
bNordic Center for Earth Evolution (NordCEE) and Institute of Biology, University of Southern Denmark, DK-5230 Odense C, Denmark;
cDepartment of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden;
dDepartment of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden;
eSchool of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287;
fDepartment of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287;
gSchool of Earth and Environment, University of Leeds, LS2 9JT, UK;
hDepartment of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138;
iNatural History Museum of Denmark, DK-1350 Copenhagen K, Denmark; and
jGeological Survey of Denmark and Greenland, DK-1350 Copenhagen K, Denmark
Contributed by Donald E. Canfield, August 17, 2010 (sent for review May 18, 2010)
Abstract
The evolution of Earth’s biota is intimately linked to the oxygenation of the oceans and atmosphere. We use the isotopic composition and concentration of molybdenum (Mo) in sedimentary rocks to explore this relationship. Our results indicate two episodes of global ocean oxygenation. The first coincides with the emergence of the Ediacaran fauna, including large, motile bilaterian animals, ca. 550–560 million year ago (Ma), reinforcing previous geochemical indications that Earth surface oxygenation facilitated this radiation. The second, perhaps larger, oxygenation took place around 400 Ma, well after the initial rise of animals and, therefore, suggesting that early metazoans evolved in a relatively low oxygen environment. This later oxygenation correlates with the diversification of vascular plants, which likely contributed to increased oxygenation through the enhanced burial of organic carbon in sediments. It also correlates with a pronounced radiation of large predatory fish, animals with high oxygen demand. We thereby couple the redox history of the atmosphere and oceans to major events in animal evolution.
Phanerozoic, molybdenum, black shale, ocean oxygenation, paleocean redox
Footnotes
1To whom correspondence should be addressed. E-mail:tdahl@fas.harvard.edu.
Author contributions: T.W.D. and E.U.H. designed research; T.W.D. and E.U.H. performed research; T.W.D., E.U.H., and G.W.G. analyzed data; E.U.H., A.D.A., D.P.G.B., B.C.G., G.W.G., A.T.N., and N.H.S. contributed new reagents/analytic tools; and T.W.D., E.U.H., A.D.A., A.H.K., and D.E.C. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at
Freely available online through the PNAS open access option.
