Tripartite Evolution of the Aerobic Biosphere, Snowball Earth, and the Lomagundi Event
Joseph Kirschvink1, Timothy Raub1, and Robert E. Kopp2
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA
2Geosciences Department, Princeton University, Princeton, NJ
The origin of the aerobic biosphere must have occurred in three steps. First, mutant microbes with oxygen-mediating enzymes evolved in environments with trace abiogenic oxygen, such as proglacial plumes “poisoned” with melted peroxide snow. Next the oxygen-evolving complex of Photosystem II developed in an oxygen-tolerant phototroph. Only then could aerobic heterotrophs, which remineralize organic carbon, evolve.
Oxygen-mediating enzymes could have evolved during the ~2.9 Ga Pongola glaciation or early in the Huronian interval, <2.45 Ga. No firm evidence exists for oxygenic photosynthesis prior to ~2.3 Ga Makganyene low-latitude glaciation. Evolution of oxygenic photosynthesis would have fostered the development of a large marine dissolved organic carbon (DOC) pool. Absent aerobic remineralization, photosynthetic oxygen could have destroyed a pre-Makganyene, 1 mb methane greenhouse in <100 kyr, plunging Earth into a “Snowball” event.
The aftermath of Paleoproterozoic glaciation is marked by exceptional inorganic carbon isotope excursion, the >10‰ Lomagundi event, beginning prior to 2206+/-9 Ma and ending precipitously ~2058 Ma. We suggest this excursion reflects an ever-growing dissolved organic carbon reservoir, and its end reflects the ultimate evolution and global spread of aerobic heterotrophy. Today, aerobic respiration requires oxygen concentrations in excess of the Pasteur point, ~1% PAL. Since the modern aerobic respiration pathway reflects two billion years of evolution, the oxygen minimum for primitive heterotrophs was likely higher. The end of the Lomagundi event may therefore serve as a paleo-oxygen constraint: between the disappearance of mass-independent fractionation of sulfur at ~2.3 Ga and the end of the Lomagundi event at ~2.06 Ga, atmospheric oxygen was likely above 0.001% PAL and below >1% PAL.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery