Use of Geology to state the timing of the Great Oxidation Event:

Use of Geology to state the timing of the Great Oxidation Event:

Oxidation of the oceans.

The timing of the Great Oxidation event has been of great debate within the scientific community, because of the different number of techniques which can be used to postulate the timing of the Great Oxidation event. However, a large number of studies have focused on the use of geological data.

The exact reason as to why scholars continue to focus on geological data to create time constraints for the great oxidation event will be explored in this blog.

The most obvious reason as to why geological data is often used is the fact that geological features are physical objects which can be studied, they do however also allow for a range of data sets to be uncovered through their geochemical analysis and correlation with other geological features which have been found to have the same age. The common method of getting the date of a rock formation is through Zircon dating, however one first has to establish if the zircon is of syngenetic or epigenetic origin. The timing of deposition is only one of the major concerns when it comes to geological features and their inclusions, reworking and metamorphism can create major timing issues.

Geochemical Analysis:

Geochemical data can also be gathered which give relative dates depending on the isotopes which one chooses to study. Crowe studied the distribution of Cr isotopes of Nsuze paleosol from the Pongola Supergroup of South Africa. Crowe used Cr isotopes because they are sensitive indicators for oxidation weathering. S-isotopes have also been used to determine the timing of the Great Oxidation event, in a study Gumsley analyzed S-isotopes from the Duitschland Formation of the Transvaal Supergroup. Gumsley's study focused on the S-isotope fractionation of mass-independent fractions as they have been found to provide the tightest constraint on the timing of the Great oxidation event. These two studies studied two different geological features and used two different isotope analysis methods which yielded two different times for the great oxidation event with Crowe's study indicating that the event occurred 300-400 million years earlier than, Gumsley's study which stated that the event occurred 2.4-2.3Ga, indicating the uncertainty that still exist when using geochemical data.

Another method which has been recently adopted by scientist is the use of bio-markers within rock formations. Bio-markers are known to be sensitive to changes in climate since they were the living organisms during that specific climatic regime and as such would be the best detectors of Oxygen production during the Great Oxidation event and other atmospheric and environmental changes.

Gumsley, went beyond just studying S-isotope fraction, he also studied the assembly of large continental mass, extensive magmatism and continental migration to near-equatorial latitudes. This was done because the extensive magmatism created large igneous provinces which would have released a large amount of greenhouse gases especially carbon dioxide, while the study of the large continental mass and its migration would allow for better correlation between different rock formation. The study of the large igneous provinces was also found to be responsible for triggering a nutrient flux which would have increased the photosynthetic activity and therefore the production of Oxygen possibly signaling the beginning of the great Oxidation, 2.5-2.4 Ga.

Even though a number of challenges do exist when it comes to using geological data as evidence for the timing of the great oxidation, when the different data sets are used together as one a more accurate and coherent date is found as to when the great oxidation event occurred 2.4 Ga.  

Reference List:

 Crowe, S.A., Døssing, L.N., Beukes, N.J., Bau, M., Kruger, S.J., Frei, R. and Canfield, D.E., 2013. Atmospheric oxygenation three billion years ago. Nature, 501(7468), pp.535-538.

 Gumsley, A.P., Chamberlain, K.R., Bleeker, W., Söderlund, U., de Kock, M.O., Larsson, E.R. and Bekker, A., 2017. Timing and tempo of the Great Oxidation Event. Proceedings of the National Academy of Sciences, 114(8), pp.1811-1816.

 Sessions, A.L., Doughty, D.M., Welander, P.V., Summons, R.E. and Newman, D.K., 2009. The continuing puzzle of the great oxidation event. Current Biology, 19(14), pp.R567-R574.