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Late Archean biospheric oxygenation and atmospheric evolution
Alan J Kaufman1, David T Johnston, James Farquhar
1Departments of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742-4211, USA.
Science (New York, N.Y.)
|September 29, 2007
Summary
The 2.5-billion-year-old Mount McRae Shale reveals the ancient oxidative sulfur cycle
Area of Science:
- Geochemistry
- Paleoceanography
- Early Earth History
Background:
- The Archean Eon (4.0 to 2.5 billion years ago) was a critical period for Earth's atmospheric and oceanic evolution.
- Understanding the early sulfur cycle is key to deciphering the conditions that preceded the Great Oxidation Event.
Purpose of the Study:
- To investigate the oxidation state of the surface ocean and atmospheric composition during the Archean.
- To determine the timing and scope of the oxidative sulfur cycle's activation.
Main Methods:
- High-resolution geochemical analyses of shale and carbonate samples.
- Sulfur isotope analysis of sedimentary rocks.
- Correlation of geological records between different continents (Australia and South Africa).
Main Results:
- The Mount McRae Shale records the first widespread and potentially permanent activation of the oxidative sulfur cycle.
- Sulfur isotope data suggest global changes in the exogenic sulfur cycle linked to atmospheric evolution.
- Ocean surface oxygenation occurred at least 50 million years before persistent atmospheric oxygenation.
Conclusions:
- The activation of the oxidative sulfur cycle was a significant global event in Earth's early history.
- Oceanic oxygenation preceded atmospheric oxygenation, indicating a complex interplay between Earth's systems.
- The findings provide crucial insights into the environmental conditions of the Archean Eon.
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