Instead, the authors suggest that the atmosphere transitioned repeatedly between two states: one with a thin, hydrocarbon haze and the other haze-free. These geochemical records were supported by models of the ancient atmosphere performed by colleagues at the NASA Astrobiology Institute, led by Dr Mark Claire (currently at the University of East Anglia, UK) and Dr Shawn Domagal-Goldman, which demonstrated how the transitions could be caused by changes in the rate of methane production by microbes.
The conditions which enabled the bi-stable organic haze to form permanently ended when the atmosphere became oxygenated some 100 million years after the sediments were laid down.
"What is most surprising about this study is that our data seems to indicate the atmospheric events were discrete in nature, flip-flopping between one stable state into another," explains co-author Dr Farquhar.
"This type of response is not all that different from the way scientists think climate operates today, and reminds us how delicate the balance between states can be."
Professor Mark Thiemens, Dean of Physical Sciences at the University of California San Diego, adds: "Another important facet of the work is that it provides insight into the formation of atmospheric aerosols, particularly organic ones.
"Besides the obvious importance for the evolution of the atmosphere, the role of aerosol formation is one of the most poorly understood components in the present day climate models. This provides a new look into this process that is quite new and valuable."
|Contact: Dr. Aubrey Zerkle|