Most of the time, scientific research seeks to build on theoretical foundations that have been carefully constructed by the wider research community, often over many years. If a theoretical framework is found to be robust, it gains widespread assent, with few interested in challenging it. Those who are attracted to the idea that science develops progressively are the least likely to talk about challenges. For them, any change is a minor modification of the theoretical edifice. Thomas Kuhn referred to these theoretical frameworks as 'paradigms', and the progressive refinement of that framework as 'normal science'. Kuhn pointed out that anomalies do not trigger the practitioners of 'normal science' to question the paradigm, but they either treat them as problems waiting to be resolved, or they ignore them altogether. In recent months, I've become aware that this phraseology and understanding of scientific activity is intensely irritating to some scientists. They appear to regard such talk as an invention of outsiders with a subversive agenda. A desire to comment on these issues has stimulated this blog, which is based on a paper authored by Walter Alvarez, an experienced and respected scientist working in the field of geology. He introduces his paper thus:
"Lightman and Gingerich (1992) argued that when a ruling theory is successful in accounting for a wide range of observations, scientists ignore observations that are not explained by the theory. They argued that such "anomalies" are only "retro-recognized" when a modification or replacement of the original theory calls attention to and explains the conflicting observations."
The "ruling theory" has been referred to above as the theoretical framework or paradigm. The quotation points out that anomalies tend to have a very low profile until solutions are found, and then the solutions are publicised widely to hail the success of the paradigm. Earth scientists generally understand paradigms. Many have lived through the Plate Tectonics revolution - which is now the ruling paradigm. Alvarez considers that a major revision of this paradigm is needed, and he points to the relevant anomalies that show all is not well.
"Such an anomaly is present in the plate tectonic theory that has dominated geological thinking for the last 30-40 yr. Plate tectonics sees subduction as able to consume an unlimited amount of dense oceanic lithosphere, but unable to continue after convergence brings two buoyant continental masses together. Buoyancy should terminate the convergence, with a new subduction zone initiated somewhere else, where it can consume oceanic lithosphere. This view persists despite evidence that at least some continental collisions have continued long after the continents first collided."
Within plate tectonic theory, there are two categories of mechanisms for driving the crustal plates: boundary forces ("slab pull" by descending plates and "ridge push" (emanating from centres of crustal generation) and drag forces (frictional forces between mantle convection cells and crustal plates). These concepts are introduced to students very early in their studies, and they have become entrenched. For examples, go here and here. For a more advanced treatment, go here. The relative contributions made by these different forces have been much discussed by scientists developing plate tectonic theory. However, firm conclusions have not been reached. If there is any consensus, it is that boundary forces are more significant than drag forces, and that slab pull is more significant than ridge push. Alvarez has the view that with plates carrying continents, drag forces are of major importance. He discusses three cases where plate movements continued long after two continental masses collided. If boundary forces were dominant, motion would cease very quickly. However, if drag forces were significant, the problems disappear. Alvarez started publishing along these lines in 1982 and claims his recent research confirms the earlier hypothesis.
"More than 25 yr ago the present author proposed that protracted collisions may be driven by traction applied at the base of deep lithospheric roots (Alvarez, 1982), and in two subsequent papers (Alvarez, 1990, 2001) used the term "continental undertow" to refer to this driving mechanism. [. . .] Although the data available at the time were insufficient to test the undertow model, there are now many relevant observations. The last section of this paper shows how the anomaly of protracted collisions can be explained by continental undertow."
It is not my intention in this blog to discuss the wider implications of the Alvarez model. My interest is in the way scientific theory develops, the way anomalies are handled and in the (often hidden) influence of dominant paradigms. What we find here in the earth sciences is frequently encountered in the field of evolutionary biology. There are many anomalies between observed data and theory, but these are typically well-known only to researchers close to both. Anomalies (in the main) do not get published until someone proposes a solution - within the ruling paradigm. In plate tectonic theories, anomalies surround the quest for driving forces able to move crustal plates and build mountains; in evolutionary biology, anomalies are pronounced when it comes to explaining how complex specified information is derived from natural causes. Darwinian mechanisms are useful for explaining antibiotic resistance but not the origin of the immune system. They are OK for changing the dimensions of finch beaks but not for constructing beaks. They have some value in elucidating industrial melanism but not for engineering structural colour in moth wings.
Wonderful music, but is there a composer? (Source here)
Researchers who propose paradigm-changing solutions do not find it easy to get their work past editors and reviewers. Intelligent Design (ID) requires a fundamental change of paradigm in the way we think about causation. Most research relating to origins admits only natural causes (naturalism), whereas ID links complex specified information to intelligent agency. ID researchers consider this is an issue that must be evaluated within science, but there are many who think otherwise! This is why Stephen Meyer's peer-refereed paper led to the removal of Richard Sternberg from the role of editor of the Proceedings of the Biological Society of Washington and the subsequent withdrawal of the paper. Other examples of editors (in other disciplines) in trouble because they were willing to publish papers that challenged the dominant paradigm were given in an earlier blog. Although there is a continuing polemic by ID-denigrators based on the supposed lack of peer-reviewed ID research, the situation is slowly changing. Nevertheless, the most important thing to realise is that the playing-field is not level and there are far too many people defending the dominant paradigm for ideological reasons. Their style of engagement with the issues suggests they are not interested in a scientific debate - their polemics are geared to ensuring naturalism is uncontested and that the worldview of science is materialism. Since doctrinaire philosophical materialists do not constitute a majority within science, it is very important that the present impasse is broken.
Protracted continental collisions argue for continental plates driven by basal traction
Earth and Planetary Science Letters, Volume 296, Issues 3-4, 1 August 2010, Pages 434-442 | doi 10.1016/j.epsl.2010.05.030
Abstract: In plate tectonic theory, collision between two continents should quickly terminate because of continental buoyancy. If convergence is to continue, it should do so at a new subduction zone where oceanic crust can be consumed. The protracted continental collisions in the Alps, Zagros, and Himalayas, which have continued to deform continental crust since the early or middle Cenozoic, are therefore anomalies in standard plate tectonic theory. It is commonly held that plates are driven by slab pull, but this does not account for the continuing Tethyan collisions where the descending slab has detached from the subducting continent. These protracted continental collisions are better explained by horizontal traction of the mantle on the base of deep continental roots, dragging the northern and southern continents together along a Tethyan axis of mantle convergence. "Continental undertow" thus resolves the collision anomaly in plate tectonics.
Tyler, D. Does Science promote atheism? ARN Literature Blog (23 July 2007)
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