Today, most researchers agree that the oxygenation of Earth’s atmosphere happened in two major steps: the first during the so-called Great Oxidation Event about 2.5-2.4 billion years ago, and the second during the Late Neoproterozoic Era around 750 to 540 million years ago. The latter is thought to have been the cause for the emergence of animals during the so-called ‘Cambrian explosion’ around 540 to 520 million years ago.
An international team of researchers led by Professor Robert Frei from the Department of Geoscience and Natural Resource Management at the University of Copenhagen has just released a study indicating evidence for the presence of small concentrations of oxygen on Earth already 3.8 billion years ago. The researchers analysed Earth’s oldest Banded Iron Formations (BIFs) from Western Greenland. …
The fact that the analyses of the BIF layers from Western Greenland show elements that require presence of oxygen in the atmosphere opens up for the possibility of evolution of the earliest primitive photosynthetic life forms as early as 3.8 billion years ago. As Robert Frei explains: “It is generally believed that the Early Earth was a completely anoxic, but our study shows that the surface of the Earth was exposed to a low oxygen atmosphere already this time. This has far reaching implications for how we investigate the pace of evolution of life and its biodiversity on our planet.” More.
In what may be part of a cultural shift in discussing such finds, Frei refrains from announcing that there might just be time for purely Darwinian evolution in that case. That’s a healthy sign. Darwinism has long functioned as a science stopper in that researchers often seemed (to judge from their media releases) to see their duty as somehow defending it against the general pattern of evidence.
The obvious difficulty is that the process of finding out what really happened is quite different from the process of defending one’s argument about it, and the confusion is a disservice to both. Especially in a case like origin of life.
Let’s just say that the whole area of how much oxygen there was on early Earth is an “active research area”—as is the question of the difference a given amount of oxygen would even make. That latter problem makes definitive conclusions difficult.
Did a low oxygen level delay complex life on Earth? (October 31, 2014)
Early Earth was indeed “extremely oxygen-poor compared to today” (January 16, 2015)
Small pre-Cambrian oxygen jump kickstarted complex life
(July 24, 2015)
Oxygen Does Not Equal Life – Implications for Abiogenesis? (September 15, 2015)
Researchers: Cyanobacteria responsible for Earth’s early oxygen
(November 28, 2015)
Animals didn’t “arise” from oxygenation, they created it, researchers say
Theory on how animals evolved challenged: Some need almost no oxygen
New study: Oxygenic photosynthesis goes back three billion years
We really should organize a panel discussion—oops, a conference—with all these people.
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Here’s the abstract:
The Great Oxidation Event signals the first large-scale oxygenation of the atmosphere roughly 2.4 Gyr ago. Geochemical signals diagnostic of oxidative weathering, however, extend as far back as 3.3–2.9 Gyr ago. 3.8–3.7 Gyr old rocks from Isua, Greenland stand as a deep time outpost, recording information on Earth’s earliest surface chemistry and the low oxygen primordial biosphere. Here we find fractionated Cr isotopes, relative to the igneous silicate Earth reservoir, in metamorphosed banded iron formations (BIFs) from Isua that indicate oxidative Cr cycling 3.8–3.7 Gyr ago. Elevated U/Th ratios in these BIFs relative to the contemporary crust, also signal oxidative mobilization of U. We suggest that reactive oxygen species were present in the Eoarchean surface environment, under a very low oxygen atmosphere, inducing oxidative elemental cycling during the deposition of the Isua BIFs and possibly supporting early aerobic biology. (public access) – Robert Frei, Sean A. Crowe, Michael Bau, Ali Polat, David A. Fowle, Lasse N. Døssing. Oxidative elemental cycling under the low O2 Eoarchean atmosphere. Scientific Reports, 2016; 6: 21058 DOI: 10.1038/srep21058