The Biology Behind Banded Iron FormationsMarch 04, 2013 / Written by: Aaron L. Gronstal
A long-enduring puzzle in the evolution of the early Earth concerns when and to what extent surface oxidation occurred. One important piece of this puzzle is determining when oxygen production began, and how early oxygen was consumed by reduced species, such as iron (Fe(II)), in the oceans. One way of tracing the Fe redox cycle through time has been studying banded iron formations (BIFs). These rock formations likely formed when Fe(II)-rich hydrothermal fluid wells up into shallow water. Fe(II) then undergoes oxidation, resulting in layers of rock that contain evidence of how and when the process happened.
It is thought that oxygen did not make up a significant portion of the atmosphere until after the ‘Great Oxidation Event,’ roughly 2.45 billion years ago. How and when oxygen was first produced on Earth before this dramatic event is still a big question. Astrobiologists, supported in part by the NAI, are now helping to solve the mystery.
The team studied BIFs in the Isua Supracrustal Belt of southwestern West Greenland. The rocks of this formation can be 3.7-3.8 billion years old, and include the oldest known BIFs on Earth. Ultimately, the isotopic signatures in the rocks suggested that oxidation of Fe(II) was most likely the result of anoxygenic photosynthesis (i.e. photosynthesis that doesn’t produce oxygen). This supports the idea that anoxygenic photosynthesis evolved before the oxygenic photosynthesis we’re all familiar with today (and which plays an important role in keeping the atmosphere breathable for us).
The research was published in the journal Earth and Planetary Science Letters. Funding came from the NSF and NASA.
Source: [Earth and Planetary Science Letters]
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