Science Literature

The true story of oxygen in the Earth's atmosphere has yet to be told. Most researchers have been brought up to believe the Miller-Urey model of abiogenesis, which required the Earth to have a reducing atmosphere to facilitate the spontaneous generation of life. The atmosphere was then considered to be neutral for over a billion years. The evolution of organisms capable of photosynthesis was the next important step, with rises of oxygen levels triggering the flowering of eukaryotes, the rise of the Ediacaran fauna and then the Cambrian Explosion. The first significant rise is understood to be abrupt and sufficient of a milestone in Earth history to warrant a name of its own. Richard Kerr's comments below lead us to the new research by Ohmoto and colleagues:

The first living things did not require oxygen to "breathe," but early life on Earth never would have gotten much beyond pond scum without free oxygen in the atmosphere. Conventional thinking has oxygen produced by photosynthesis gaining the upper hand 2.4 billion years ago, nearly halfway into Earth history. But new laboratory results reported in tomorrow's issue of Science challenge the late arrival of this "Great Oxidation Event."

Ocean sediments deposited prior to the GOE contain red hematite - fully oxidised iron. (Credit: Hiroshi Ohmoto, source here)

Ohmoto's hypothesis is that significant quantities of free oxygen were present in Earth's atmosphere prior to the GOE. He represents a minority position, but he continues to provide leadership in this area and a regular stream of relevant papers. One of the issues concerns patterns found in sulphur isotopes. Here is Kerr again:

"Then in 2000, geochemist James Farquhar of the University of Maryland, College Park, came up with a nifty technique involving sulfur isotopes. The proportion of one isotope to another of the same element can change during a chemical reaction. Normally, the change depends on the masses of the isotopes. But Farquhar found isotopic shifts among three sulfur isotopes before 2.4 billion years ago that hadn't depended on isotope mass. As far as anyone knew, such "mass-independent fractionation" (MIF) could have happened only under solar ultraviolet radiation in an oxygen-free atmosphere - and MIF sulfur disappeared 2.4 billion years ago."

The new paper, with Farquar as one of the co-authors, proposes an alternative origin for these isotopic signatures that keep the door open for discussion of an early, oxygen-rich atmosphere.

"The significance of this finding is that an abnormal isotope fractionation (of sulfur) may not be linked to the atmosphere at all," says Yumiko Watanabe, research associate [and co-author], Penn State. "The strongest evidence for an oxygen poor atmosphere 2.4 billion years ago is now brought into question."

Several papers have appeared in recent years hinting at atmospheric oxygen prior to the GOE. Direct evidence of photosynthesising organisms goes back to rocks dated to 2.7 Ga, and indirect evidence even earlier. In February this year, supporting evidence comes from the presence of fully oxidised iron (hematite) in rocks from Western Australia:

Then, the minimum pO2 of the pre-2.76-Ga atmosphere can be estimated to be 3 x 10-3 atm or 1.5% of the present atmospheric value. This scenario of oxygenated atmosphere is, however, inconsistent with a current popular model for atmospheric evolution based on the MIF-S record in sedimentary rocks.

Hematite minerals have demonstrated an abundance of oxygen during the time of deposition. In an oxygenated world, it is easy to find places that are reducing or neutral (we have them today). What is not easy is to explain regions rich in oxygen within a reducing or neutral world. This gives a strong case for early oxygenation. "This is at least a possibility that we should be thinking about," Ohmoto says and adds, "I feel the findings we made fit nicely to what I've been saying for years."

Why are these research findings of interest to ID scientists? The main reason concerns the "evolutionary storytelling" mindset that afflicts many researchers. It is important to them that the findings of research fit within the evolutionary paradigm. There is a consensus that the abiogenesis scenario, followed by a step-by-step evolution of the atmosphere, is a given. Within this, another evolutionary story, of fauna and flora, can be constructed. It all fits together beautifully (they think). Ohmoto's research breaks this mould, pushing back the origin of complex photosynthesising organisms into the Early Archaean and reducing the evidential base for abiogenesis from tenuous to zero. This puts extreme constraints on thinking about the origins of biological complexity - as ID scientists have often pointed out. Design, rather than stochastic processes, is therefore indicated.

Anomalous Fractionations of Sulfur Isotopes During Thermochemical Sulfate Reduction
Yumiko Watanabe, James Farquhar, and Hiroshi Ohmoto
Science, 324, 17 April 2009: 370-373.

Abstract: Anomalously fractionated sulfur isotopes in many sedimentary rocks older than 2.4 billion years have been widely believed to be the products of ultraviolet photolysis of volcanic sulfur dioxide in an anoxic atmosphere. Our laboratory experiments have revealed that reduced-sulfur species produced by reactions between powders of amino acids and sulfate at 150 to 200 degrees C possess anomalously fractionated sulfur isotopes: [. . .]. These results suggest that reactions between organic matter in sediments and sulfate-rich hydrothermal solutions may have produced anomalous sulfur isotope signatures in some sedimentary rocks. If so, the sulfur isotope record of sedimentary rocks may be linked to the biological and thermal evolution of Earth in ways different than previously thought.

Primary haematite formation in an oxygenated sea 3.46 billion years ago
Masamichi Hoashi, David C. Bevacqua, Tsubasa Otake, Yumiko Watanabe, Arthur H. Hickman, Satoshi Utsunomiya & Hiroshi Ohmoto
Nature Geoscience, Published online: 15 March 2009 | doi:10.1038/ngeo465

Abstract: The timing of the origin of photosynthesis on the early Earth is greatly debated. It is generally agreed, on the basis of the presence of biological molecules found in shales from the Hamersley Basin, Australia, that oxygenic photosynthesis had evolved 2.7 billion years (Gyr) ago. However, whether photosynthesis occurred before this time remains controversial. Here we report primary haematite crystals and associated minerals within the marine sedimentary rocks preserved in a jasper formation of the Pilbara Craton, Australia, which we interpret as evidence for the formation of these rocks in an oxygenated water body 3.46 Gyr ago. We suggest that these haematite crystals formed at temperatures greater than 60 degrees C from locally discharged hydrothermal fluids rich in ferrous iron. The crystals precipitated when the fluids rapidly mixed with overlying oxygenated sea water, at depths greater than 200 m. As our findings imply the existence of noticeable quantities of molecular oxygen, we propose that organisms capable of oxygenic photosynthesis evolved more than 700 million years earlier than previously recognized, resulting in the oxygenation of at least some intermediate and deep ocean regions.

See also:

Berardelli, P. Oxygenated Oceans Go Way, Way Back, ScienceNOW Daily News, 16 March 2009

Kato, Y., Suzuki, K., Nakamura, K., Hickman, A.H., Nedachi, M., Kusakabe, M., Bevacqua, D.C. and Ohmoto, H. Hematite formation by oxygenated groundwater more than 2.76 billion years ago, Earth and Planetary Science Letters, Volume 278, Issues 1-2, 15 February 2009, Pages 40-49 | doi:10.1016/j.epsl.2008.11.021

Kerr, R. Great Oxidation Event Dethroned? Science, 324, 17 April 2009: 321.