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The Oxygen Catastrophe and Copper

Monday, April 18, 2016 19:17

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The Great Oxygenation Event (GOE), also called the Oxygen Catastrophe, Oxygen Crisis, Oxygen Holocaust, Oxygen Revolution, or Great Oxidation, was the biologically induced appearance of dioxygen (O2) in Earth’s atmosphere. Although geological, isotopic, and chemical evidence suggest that this major environmental change happened around 2.3 billion years ago (2.3 Ga) actual causes and the exact date of the event are very contested amongst the scientific community. It has been argued that current geochemical and biomarker evidence for the development of oxygenic photosynthesis before the Great Oxidation Event has been mostly inconclusive

“Our findings make it possible to reconstruct nutrient content in early marine settings and demonstrate that the iron-rich content of the early oceans must have severely restricted the availability of nutrients important for life”, says Dr Ernest Chi Fru of Stockholm University, who has led the research group.

The study suggests a gradual shift in mainly negative copper isotopic composition of marine carbon-rich sediments, beginning at 2.4 billion years ago (Ga), to permanently positive values after 2.3 Ga. The authors argue that the change reflects the drawn-out nature of the Great Oxidation Event (GOE), when atmospheric oxygen content went from virtually nothing, starting at 2.4 Ga, to peak at near present day levels by 2.3 Ga.

Photo: Catarina Nilsson/Mostphotos

Fundamentally, the high iron content of the early oceans are suggested to have played a critical role in determining trace metal availability, whereby copper levels increased when decreasing marine iron content fell by about 1 000 times after the GOE. The research has been made by examining carbon-rich rocks deposited at the bottom of ancient oceans 2.66-2.1 billion years ago.

“The appearance of oxygen in the atmosphere is one of the most important changes in Earth’s geological history that enabled the evolution of oxygen based life. Understanding the chemistry of the very early oceans and how nutrients were made available, guide our steps towards understanding the processes that govern our own evolution”, says Dr Ernest Chi Fru of Stockholm University.

O₂ build-up in the Earth’s atmosphere. Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga).
Stage 1 (3.85–2.45 Ga): Practically no O₂ in the atmosphere.The atmosphere was entirely anoxic.
Stage 2 (2.45–1.85 Ga): O₂ produced, and rose to values of 0.02 and 0.04 atm,but absorbed in oceans and seabed rock.
Stage 3 (1.85–0.85 Ga): O₂ starts to gas out of the oceans, but is absorbed by land surfaces.There wasn’t a significant change in terms of oxygen level.
Stages 4 and 5 (0.85–present): O₂ sinks filled and the gas accumulates

Credit: Heinrich D. Holland

The study provides a tool for tracking how oxygen levels have fluctuated through Earth’s history and the evolutionary changes that accompanied these fluctuations.

“Our study is highlighting how the isotopic ratios of copper can unlock the evolution of Earth’s early oceans from being oxygen-poor to more like they are today. We now hope to apply this technique to understanding other major geological events in the Earth’s history”, says Professor Dominik Weiss, co-author from Imperial College London.

Oceanic cyanobacteria, having developed into multicellular forms more than 2.3 billion years ago (approximately 200 million years before the GOE), became the first microbes to produce oxygen by photosynthesis. Before the GOE, any free oxygen they produced was chemically captured by dissolved iron or organic matter. The GOE was the point when these oxygen sinks became saturated and could not capture all of the oxygen that was produced by cyanobacterial photosynthesis. After the GOE, the excess free oxygen started to accumulate in the atmosphere.

Oceanic cyanobacteria

Credit: Doc. RNDr. Josef Reischig, CSc.

The increased production of oxygen set Earth’s original atmosphere off balance. Free oxygen is toxic to obligate anaerobic organisms, and the rising concentrations may have wiped out most of the Earth’s anaerobic inhabitants at the time. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earth’s history. Further evidence from spikes in chromium show that cyanobacteria were responsible for the oxygen.

Contacts and sources:
Dr Ernest Chi Fru
Stockholm University

The project was carried out by an international team of researchers from Sweden, England, France and Canada, led by Dr Ernest Chi Fru of Stockholm. It was funded by the European Union under an Intra-European Marie Curie Fellowship and a European Research Council starting grant to the lead author.

The article Cu isotopes in marine black shales record the Great Oxidation Event was recently published in The Proceedings of the National Academy of Sciences, U.S.A.

Source: http://www.ineffableisland.com/2016/04/the-oxygen-catastrophe-and-copper.html

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