Geology Controversies

I find it interesting to read about geology controversies and the rationale underpinning the opposing hypotheses, that provides insight into the evolution of the 'discussions' to a general consensus. The greater the controversy, the more likelihood it has of making it to a wider audience and that is when someone with sufficient perspective can outline the respective arguments in terminology a non specialist can understand. Geology controversies tend to be long running affairs as entrenched parties present more evidence to substantiate their hypotheses and refute opposing hypotheses. When the evidence comprises actual bedrock outcrops, there is also the opportunity to walk the same sections and understand better their significance.

Some older major controversies have been well documented with books written to provide an historical overview of the controversy. Two books that I found particular interesting as they cover rocks in areas that I have visited, deal comprehensively two notable 19th Century controversies in the UK :

The Cambrian Silurian controversy  ~ Ordering geological stratigraphy which ultimately resulted in the establishment of the Ordovician.



Highlands Controversy ~ A bitter dispute on geological stratigraphy and a triumph of geological fieldwork to elucidate the tectonic structure.



It would be reasonable to suggest that geologists have a greater appetite for robust discussion than other sciences, which does add a certain frission to reading a geology paper on a controversial topic. One current long running 'heated' controversy is Archean Plate tectonics and as an example of robust discussion I have cherry picked some statements from the Introduction to a paper by Warren B. Hamilton in a memoir by the Geological Society of America.

"This essay is a study in alternatives. Most current interpretations of geodynamics and of evolution of Earth are forced to fit popular but dubious assumptions that Earth fractionated slowly and is still largely unfractionated, and that rocks of all ages must be explained with plate-tectonic processes combined with plumes rising from basal mantle. The data accord better with opposite interpretations. Earth largely fractionated very early in its history, plate tectonics did not begin operating until late Proterozoic time, and deep-mantle plumes do not operate now and did not affect the Archean Earth."

"Our planet had a hot, violent beginning, and has evolved only slowly toward its present dynamic patterns. The geologic record of the young Earth differs profoundly from that of the modern one in crustal architecture and in rock types, assemblages, and structural and magmatic histories."

"I have seen hundreds of exposures of early Paleozoic to middle Tertiary subduction mélanges around the world, but not a suggestion of one in the Archean."

"I see no plate-tectonic interactions in the Archean record. Most plate-tectonic interpretations for the Archean are based on weak compositional analogies with modern rocks of known settings, or with imagined products of hypothetical plate-related settings that have no modern analogues. Although this is a valid approach in the search for explanations, its implicit predictions are not then tested against geologic data." 

"The cartoons drawn to illustrate such schemes (e.g., Kerrich and Polat, 2006) are unrelated to anything seen on the ground." 

"Modern-mode plate tectonics, with high-pressure, low-temperature metamorphism in its sutures, began only much later, in Neoproterozoic or very early Paleozoic time (Stern, 2005, 2007; Tsujimori et al., 2006)." 

Hamilton, W.B., 2007, Earth’s first two billion years—The era of internally mobile crust, in Hatcher, R.D., Jr., Carlson, M.P., McBride, J.H., and Martínez Catalán, J.R., eds., 4-D Framework of Continental Crust: Geological Society of America Memoir 200, p. 233–296  

In the next post I will look at an area of the UK that with an exposure of Archean bedrock and the current controversies associated with it.