A theory of the Earth: Hutton and Humpty Dumpty and Holmes

Abstract

Abstract Paradoxes can be viewed as a bother or as a rich source of information. Paradoxes, fallacies and logical inconsistencies, along with the unstated assumptions behind old worldviews often form the foundation for a new worldview. This is where science differs from myth and just-so stories. Mantle dynamicists and geochemists have developed a worldview that, in many respects, is incompatible with modern theories of planetary accretion, geodynamics and geophysics, and with the geological context of volcanoes. A primordial undegassed mantle, as both the furnace and the fuel of midplate volcanoes, occupies a central role in the geochemical models. Although modern data alone are sufficient to overturn this view, it is interesting to address it in terms of its own assumptions, fallacies and inconsistencies, and the history of ideas. This is a vast field, so, in honour of James Hutton, I focus on volcanoes, their products, their causes and their sources. The following axioms are developed which point toward a different kind of world from the pristine primordial worldviews and the plume paradigm. • Linear volcanic chains delineate the stress field, not the displacement field, of the lithosphere. • Lithospheric architecture, not the core-mantle boundary, dictates the planform of convection in the mantle. • Incipient melting is the normal state of the upper mantle. • The lower mantle is depleted in the heat producing elements compared to the crust, upper mantle and the bulk silicate Earth. • The Earth is depleted in volatile elements. • High 3 He/ 4 He ratios in mantle materials imply a deficit of 4 He. • Primordial heat contributes a significant part of the Earth’s heat flow. These axioms [ A ] are the inverse of the assumptions of the plume and primordial mantle paradigms [not- A ] and the new and the old views are to each other as looking-glass worlds. An ‘axiom’ is a self-evident truth or an established rule. It is also an undemonstrated proposition concerning an undefined set of elements and relationships. The above ‘axioms’ [ A ] are not true axioms but [not- A ] provide the axiomatic framework of the current world model. These [not- A ] propositions are treated as self-evident truths so [ A ] can also be called axioms, even though they are falsifiable. The prevailing worldview, the ‘standard model’, attributes both melting and volcanic chains to deep mantle upwellings controlled by the bottom of the system with most of the original radioactivity and volatile inventory of the Earth in the deep mantle. This is not only inconsistent with modern data but also with the previous worldview embedded in the axioms. These axioms have not been pushed out by better ideas, or falsified; they have simply been overlooked or forgotten. Mantle dynamics is controlled from the top, not the bottom.