It is not known whether environmental O2 levels increased in a linear fashion or fluctuated dynamically between the evolution of oxygenic photosynthesis and the later Great Oxidation Event. New rhenium-osmium isotope data from the late Archean Mount McRae Shale, Western Australia, reveal a transient episode of oxidative continental weathering more than 50 million years before the onset of the Great Oxidation Event. A depositional age of 2495 ± 14 million years and an initial 187Os/188Os of 0.34 ± 0.19 were obtained for rhenium- and molybdenum-rich black shales. The initial 187Os/188Os is higher than the mantle/extraterrestrial value of 0.11, pointing to mild environmental oxygenation and oxidative mobilization of rhenium, molybdenum, and radiogenic osmium from the upper continental crust and to contemporaneous transport of these metals to seawater. By contrast, stratigraphically overlying black shales are rhenium- and molybdenum-poor and have a mantle-like initial 187Os/188Os of 0.06 ± 0.09, indicating a reduced continental flux of rhenium, molybdenum, and osmium to seawater because of a drop in environmental O[subscript 2] levels. Transient oxygenation events, like the one captured by the Mount McRae Shale, probably separated intervals of less oxygenated conditions during the late Archean.
For this creative project, I have decided to highlight two memories from my time in Tanzania. I have titled it Empty but Full: Experiences While Teaching In Eastern Africa. These memories are the ones that I think about the most. They are the ones that I think about unconsciously. Everything that I do reminds me of them. I often attempt to repress these memories. I try to think of the happier times while I was over there. However, no matter what I do, what I try to distract myself with, they always seem to bubble to the surface. These are not happy memories. They do not make me smile and they often make me cry to to think about. Even though I had a tough time writing these, I feel that these are moments that people should know about. Moments that people can learn from. This is why I have decided to write about these memories. These stories are raw and they do not pull any punches. They are exactly what I witnessed and exactly what I was feeling those dark moments. When I close my eyes at night, my mind often goes back to that vibrant green jungle where I became a changed man.