"Is it possible that we did not evolve from apes but were created by something else using ape DNA through many failures that we have in our museums?"
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Evolution of Oxygen, Biogeochemical Cycles, and Habitability
PI: David Catling
Geochemical differences between the ancient and modern Earth indicate two stepwise increases in atmospheric oxygen levels. The 2nd increase occurred 750-580 million years ago. This coincides with the earliest biomarker evidence for animal life and concludes prior to the emergence of Ediacaran and Cambrian animals, plausibly acting as their precursor. However, what caused the 2nd rise of oxygen remains a major unsolved puzzle of Earth history. Biogeochemical models have elucidated the atmospheric history and geochemical data of the last 500 million years, but comparable models for Neoproterozoic era (1000-542 Ma) that encompasses the 2nd rise of O2 are largely lacking. On a related but different topic, high levels of O2 along with chemical disequilibrium of planetary atmospheres have both been proposed as remotely detectable biosignatures of life on habitable exoplanets. Through two tasks, we will investigate both issues: the cause of the 2nd rise of O2 and the quantification of atmospheric chemical disequilibrium as a possible biosignature.
In Task 1, we will quantitatively examine proposed causes of the 2nd rise of O2. This change is linked to an increase of marine sulfate and a major shift in the sulfur cycle. Consequently, we will develop a time-dependent sulfur cycle model for the Neoproterozoic. This model will be integrated with a pre-existing code that calculates atmospheric oxygen levels in response to Earth system redox fluxes. We will also integrate a capability to track isotopes of carbon and sulfur in order to compare with data. Finally, we will model the photochemical changes in the atmosphere associated with the 2nd rise of O2 to assess the magnitude of a possible decrease in methane, which could be linked to climatic change. In Task 2, we will develop a general technique to quantify the chemical disequilibrium in any planetary atmosphere as a possible biosignature metric. We will rigorously assess the metric through application to the atmospheres of the ancient and modern Earth in different stages of oxygenation, Solar System planets, and possible exoplanets. By quantifying disequilibrium, we will determine the extent to which it could be useful in distinguishing life from non-life when applied to future compositional information of exoplanet atmospheres.
The results of Task 1 will be a new framework for understanding the 2nd rise of oxygen and testing suggestions for its causes. The result of Task 2 will be the most detailed study to date of how thermodynamic disequilibrium of atmospheric gases can be used to detect life remotely.
May 16, 2012
