New Evidence Supports 'Snowball Earth' as Trigger for Early Animal Evolution
ScienceDaily (Oct. 27, 2010) — A team of scientists, led by biogeochemists at the University of California, Riverside, has found new evidence linking "Snowball Earth" glacial events to the rise of early animals.
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Lead author Noah Planavsky examines sedimentary rocks (diamictite) in Northern Norway that were deposited in the aftermath of one of the widespread 'Snowball Earth' glacial events. (Credit: Lyons lab, UC Riverside)
The controversial Snowball Earth hypothesis posits that the Earth was covered from pole to pole by a thick sheet of ice lasting, on several occasions, for millions of years. These glaciations, the most severe in Earth history, occurred from 750 to 580 million years ago. The researchers argue that the oceans in the aftermath of these events were rich in phosphorus, a nutrient that controls the abundance of life in the oceans.
The UC Riverside team and colleagues tracked phosphorus concentrations through Earth's history by analyzing the composition of iron-rich chemical precipitates that accumulated on the seafloor and scavenged phosphorus from seawater. Their analyses revealed that there was a pronounced spike in marine phosphorus levels in the mid-Neoproterozoic (from ~750 to ~635 million years ago).
To explain these anomalously high concentrations, the researchers argue that the increase in erosion and chemical weathering on land that accompanied Snowball Earth glacial events led to the high amounts phosphorus in the ocean. The abundance of this nutrient, which is essential for life, in turn, led to a spike in oxygen production via photosynthesis and its accumulation in the atmosphere, facilitating the emergence of complex life on Earth.
Study results appear in the Oct. 28 issue of Nature.
"In the geological record, we found a signature for high marine phosphorus concentrations appearing in the immediate aftermath of the Snowball Earth glacial events," said Noah Planavsky, the first author of the research paper and a graduate student in the Department of Earth Sciences. "Phosphorus ultimately limits net primary productivity on geological timescales. Therefore, high marine phosphorus levels would have facilitated a shift to a more oxygen-rich ocean-atmosphere system. This shift could have paved the way for the rise of animals and their ecological diversification. Our work provides a mechanistic link between extensive Neoproterozoic glaciations and early animal evolution."
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Nature 467, 1088-1090 (28 October 2010) | doi:10.1038/nature09485; Received 19 November 2009; Accepted 2 September 2010; Published online 27 October 2010
The evolution of the marine phosphate reservoir
Noah J. Planavsky1,2, Olivier J. Rouxel2,3, Andrey Bekker4, Stefan V. Lalonde5, Kurt O. Konhauser5, Christopher T. Reinhard1 & Timothy W. Lyons1
Department of Earth Sciences, University of California, Riverside, California 92521, USA
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institute, Woods Hole, Massachusetts 02543, USA
Université Européene de Bretagne, European Institute for Marine Studies, Technopôle Brest-Iroise, Place Nicolas Copernic, 29280 Plouzané, France
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
Correspondence to: Timothy W. Lyons1 Email: timothy.lyons@ucr.edu
Phosphorus is a biolimiting nutrient that has an important role in regulating the burial of organic matter and the redox state of the ocean–atmosphere system1. The ratio of phosphorus to iron in iron-oxide-rich sedimentary rocks can be used to track dissolved phosphate concentrations if the dissolved silica concentration of sea water is estimated2, 3, 4, 5. Here we present iron and phosphorus concentration ratios from distal hydrothermal sediments and iron formations through time to study the evolution of the marine phosphate reservoir. The data suggest that phosphate concentrations have been relatively constant over the Phanerozoic eon, the past 542 million years (Myr) of Earth’s history. In contrast, phosphate concentrations seem to have been elevated in Precambrian oceans. Specifically, there is a peak in phosphorus-to-iron ratios in Neoproterozoic iron formations dating from ~750 to ~635 Myr ago, indicating unusually high dissolved phosphate concentrations in the aftermath of widespread, low-latitude ‘snowball Earth’ glaciations. An enhanced postglacial phosphate flux would have caused high rates of primary productivity and organic carbon burial and a transition to more oxidizing conditions in the ocean and atmosphere. The snowball Earth glaciations and Neoproterozoic oxidation are both suggested as triggers for the evolution and radiation of metazoans6, 7. We propose that these two factors are intimately linked; a glacially induced nutrient surplus could have led to an increase in atmospheric oxygen, paving the way for the rise of metazoan life.
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NOTA IMPERTINENTE DESTE BLOGGER:
Há 750 milhões de anos não havia nenhum ser humano para provocar anropogenicamente esta que foi uma das mais violentas mudanças climáticas que a Terra sofreu. Sem humanos, não havia indústria, nem carros, y otras conveniências tais.
E aqui a pergunta: se um evento cataclísmico desse porte ocorreu sem a ação humana, qual a ciência climatológica [não existe isso, e se disserem, não acredite, está mais para alquimia] que pode nos assegurar cientificamente que as mudanças climáticas são antropogenicamente provocadas???
Vade retro Al 'Apocalipse' Gore e Pachauri [que ainda não dançou a Pachanga, e se mantém firme e forte no comando do IPCC, apesar de... (preencher as lacunas)].
