"In winter, when water freezes, how does the freezing ice help the marine life/plants inside lakes, rivers, and oceans to surive? "
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Seminar Detail
Biogeochemical responses to the changing Paleoproterozoic atmosphere
Presenter: Dominic Papineau ()
September 13, 2004 01:00 PM Pacific
Planetary scale changes in the redox state of the Paleoproterozoic
atmosphere and hydrosphere have profoundly affected the evolution of life on
Earth. The accumulation of oxygen in the atmosphere is the result of
oxygenic photosynthesis, which is thought to have evolved prior to 2.7 Ga.
The Paleoproterozoic carbon cycle has experienced dramatic variations with
world-wide carbonate occurrences that recorded excursions of isotopically
heavy carbon, consistent with the oxygenation of the atmosphere. The
nitrogen cycle also appears to have evolved from the anoxic Archean
atmosphere, where biological nitrogen fixation was dominant, to the
oxygenated Proterozoic and Phanerozoic terrestrial surface where
denitrification became dominant. The oxygenation of the atmosphere can be
traced with multiple sulfur isotopes, which are known to fractionate
independently from their masses during the ultraviolet photolysis of reduced
or oxidized sulfur gases. Mass independently fractionated (MIF) sulfur
isotopes often occur in Archean sedimentary sulfides and sulfates, but very
rarely in rocks younger than 2.0 Ga. This observation is consistent with
the transition from an anoxic Archean atmosphere devoid of an ozone layer to
an oxygenated atmosphere more similar to the modern atmosphere. New
multiple sulfur isotopic analyses (32S, 33S, and 34S) of sulfides by
multicollector secondary ion mass spectrometry confirm that the MIF signal
is lost during the Paleoproterozoic. Variations in the sulfur isotopic
composition of Paleoproterozoic sulfides (d34S) may indicate periods of
higher or lower seawater sulfate concentration and may help to understand
the biogeochemical changes induced by the accumulation of atmospheric
oxygen.Participation Instructions
http://nai.arc.nasa.gov/seminars/instructions.cfm
December 21, 2007
The Director’s Seminar series features talks from scientists who are invited by the NAI Director to present their research results to the community. A primary goal of the seminars is to encourage interdisciplinary collaboration across NAI teams and within the astrobiology community at large.
Team Overview Seminars describe the work of the fourteen NAI teams and NAI Central. They offer an opportunity to find out more about the science, E/PO and other activities being performed by the NAI teams and the NAI Central office.
The Forum for Astrobiology Research (FAR) provides an opportunity for graduate students to present their research results and to meet as a student community for networking and mutual support.
The University of Washington seminar series is hosted by the NAI Virtual Planetary Lab (VPL) team from the UW campus in Seattle.
