Archive: The Downfall of Uniformitarianism (2003)
This CEH entry from 20 years ago argues that accepted geology is wrong about mantle plumes.
Note: some links in the article may no longer work.
The Downfall of Uniformitarianism 11/04/2003
Can major paradigm shifts occur in science today? Check this one out.
You’ve seen it on TV science programs and in textbooks: plumes of hot magma from deep in the Earth’s mantle rise through the crust and erupt on the surface (the IMAX movie Yellowstone has computer graphics of the whole process). Perhaps you’ve seen animations of the Hawaiian Islands riding over a “hot spot” and building its chain of volcanoes over millions of years on its slow, drifting journey. Textbook diagrams show cross-sections of Earth’s crust, with lava erupting from channels rooted deep in the mantle, while crustal plates float and drift atop deep convection currents.
That’s all defunct now, and so is a lot of the uniformitarian dogma associated with it, claims Warren B. Hamilton (Colorado School of Mines), in an extensive article in this month’s GSA Today.1 Uniformitarianism is out, catastrophism is in. Now, don’t get the idea Hamilton denies the Earth is billions of years old; he still accepts the 4.567 billion year figure, the condensation of Earth from a solar nebula, and all that. But he replaces Charles Lyell’s old premise “the present is the key to the past” with a new picture that seems to pay homage to Stephen Jay Gould. He calls his model “Punctuated Gradualism.” How serious is the subject? Enough for him to entitle his paper, “An Alternative Earth,” and for it to get prominent press in a journal of the world’s leading geological society.
Here’s the overview Hamilton provides of his paradigm, and the timeline of catastrophic events he now envisions (Note: Ga = giga-annum, i.e., a billion years).
“The Earth described here differs profoundly from that accepted as dogma in most textbooks and research papers. Crust and upper mantle have formed a mostly closed system throughout geologic time, and their dramatic temporal changes are responses to cooling. The changing processes define a Punctuated Gradualism and not Uniformitarianism. Major stages in Earth evolution:
- 4.567–ca. 4.4 Ga. Hot accretion and major irreversible mantle fractionation. Giant bolides continue to ca. 3.9 Ga.
- 4.4–3.5 Ga. Era of nearly global felsic crust, too hot and mobile to stand as continents.
- 3.5–2.0 Ga. Granite-and-greenstone era. Permanent hydrosphere. Old crust cooled to density permitting mafic melts to reach surface. Diapiric batholiths mobilized from underlying old crust.
- 2.0 Ga–continuing. Plate tectonic era. Distinct continents and oceans. Top-down cooling of oceanic lithosphere enables subduction that drives plates, forces spreading, and mixes continental as well as oceanic crust into upper mantle.”
While much of this timeline looks standard, some of the underlying changes to assumptions are striking. The rhetoric is also notable in that the new view is revolutionary, and overthrows long-held beliefs about uniformitarianism and plate tectonics. Notice his confidence in the abstract: “Plumes from deep mantle, subduction into deep mantle, and bottom-up convective drive do not exist.” In his Overview, he outlines how the old ideas have died:
“The conventional model (e.g., Turcotte and Schubert, 2002) of Earth’s evolution and dynamics postulates that most of the mantle is little fractionated, major differentiation continues, and continental crust has grown progressively throughout geologic time; through-the-mantle convection operates, lithosphere plates are moved by bottom-driven currents, and plumes rise from basal mantle to surface; and plate tectonics operated in early Precambrian time. All of these conjectures likely are false. They descend from speculation by Urey (1951) and other pioneers, reasonable then but not now, that Earth accreted slowly and at low temperature from fertile chondritic and carbonaceous-chondritic materials, heated gradually by radioactive decay and core segregation, and is still fractionating.”
Hamilton explains that “The notion of a cold, volatile-rich, young planet has long since been disproved,” but its corollary of an unfractionated [i.e., homogeneous, and therefore fluid] lower mantle no longer can stand up to the facts; “major constraints” now rule this view out in favor of shallow crustal activity from the upper mantle and crust. This includes radioactive heating, of which he says, “Earth’s heat loss, now largely of radiogenic heat, is much overstated in the standard model.” He suggests a value 70% the earlier one, and states, “thermodynamic and mineral-physics data require that nearly all radioactivity be above 660 km (Hofmeister and Criss, 2003),” i.e., no deeper than 400 miles. At that depth there is a discontinuity that could not be breached by a magma plume.
In short, most volcanic activity and crustal movement is shallow, and plate tectonics started much later than assumed. What are some of the ramifications geologists will have to consider if Hamilton’s “Alternative Earth” becomes the new textbook orthodoxy? Some are technical, but here are a few for the casual reader:
- The heat of volcanism is shallow, not deep. The early crust did not form continents till much later than earlier assumed.
- Plate tectonics began later. “Plate tectonics did not operate within preserved Archean crust,” Hamilton asserts, and began (in his timeline) at 2.0 Ga.
- Plate tectonics operates differently. “What drives plates?” he rhetorically asks. ”Most published models and explanations overlook known plate characteristics and behavior and instead elaborate false assumptions.” He describes subduction and seafloor spreading as shallow processes, not driven by convection from deep within the mantle. Notice how he derides those who have fudged their data to argue for deep mantle motions:”Many published models are misleading: colors are saturated for lower-mantle anomalies one-tenth or one-fifth the amplitude of upper-mantle ones, huge unsampled volumes are assigned average values or populated with spherical-harmonic artifacts, illusory continuity is generated by severe smoothing and sharpening, cross sections are placed where subduction interpretations look most plausible. Models account for only a few tenths of traveltime variance, and have not been tested by attempting to squeeze solutions back into upper mantle. Nonsubduction alternatives receive little evaluation.”
- No more mantle plumes allowed. Of the prototypical Hawaiian Islands case, he says, “There, in its only rigorously testable locale, the fixed-plume concept is falsified.” How do supporters typically respond? He claims, “Plume advocates respond to such refutations by making their conjectures ever more complex, unique to each example, and untestable.” Yet beyond this, “All other geochemical, kinematic, and tectonic plume rationales derive from the misinterpretation that Hawaii stands atop a plume.”
- Pure magma cannot reach the surface. “Pro-plume conjectures assume wrongly that magmas are transported from melting sites to surface without modification, thereby preserving elemental and isotopic ratios of sources,” he chides. He is emphatic that this assumption is no longer supportable: “Thermodynamics and phase petrology, including cotectic compositions of basalts and presence of underlying cumulates, prove that instead melts are profoundly modified before eruption (O’Hara and Herzberg, 2002).” Hamilton continues to take opponents to task, accusing them of circular reasoning and flawed methodologies.
- Island chains can form at once. Rather than growing by drift of plates over hotspots, they form over “crackspots” that allow heat to the surface: “Island alignments, in this view, reflect regional stresses, perpetuation of directions once established, and lithosphere properties.” Otherwise plume advocates have to explain how the Hawaiian chain made a 60-degree turn.
- Recycled plate slabs are complex. “Temperature, age, and isotopic ratios of sunken slabs vary regionally.” What applies hither may not apply thither or yon.
- Plate tectonics is top-down, not bottom-up. Cooling at the top drives subduction, producing shallow cycles in the upper crust, all happening above 660 km. It also allows for rotation of plates, impossible under the bottom-up view, which assumed there could be no net rotation: “The no-net-rotation framework minimizes motions of ridges and randomizes motions of subduction hinges so that many roll forward–impossible with gravity drive. The lack of rational kinematics in these popular frameworks fosters acceptance of mysterious bottom drives,” he says.
These are just a few of the ramifications mentioned by Hamilton. Other consequences of this “Alternative Earth” with its shallow motions and shallow heating may become evident if the view becomes mainstream, which appears inevitable (see Aug. 20 and Apr. 1 headlines).
1Warren B. Hamilton, “An Alternative Earth,” GSA Today, Vol. 13, No. 11, pp. 4-12.; DOI: 10.1130/1052-5173(2003)013<0004:AAE>2.0.CO;2.
What’s most interesting about this story is not the new model, which may become the next discarded paradigm in the future, but the frank and revealing charges made against proponents of the old model: that they cheated, lied, and used irrational arguments to prop up their beliefs. Is that possible in science? You read it right here.Creationists have similarly argued against the standard model for a long time and maybe now are getting some comeuppance. Dr. Walter Brown, for instance, has complained that deep mantle magma plumes are impossible, because the kinematics and thermodynamics would force the channels shut (see his paragraph on volcanoes and lava). Volcanism, therefore, must occur at shallow depths.
What can we learn from this paradigm shift? Make no mistake: confident-sounding scientific models, replete with professional jargon, (maybe even this one here – cf. 11/14/2002 headline), are written by fallible human beings. Like a hollow idol on a pedestal, a popular theory about the unobservable past might gleam in the sun for awhile, till toppled by tremors of fact. Broken on the ground, it is swept away and forgotten, and then a new hollow idol takes its place. Why hollow? Because no observer was there to corroborate the processes or the vast periods of time they are assumed to take. Remember Grand Canyon! It was the prototypical case of a phenomenon requiring millions of years, yet now the consensus is growing that it was formed catastrophically and recently (see 07/22/2002 headline). It should seem foolish to place one’s faith in the conjectures of mortals instead of in the testimony of an authoritative Eyewitness.
Those not beholden to secular geological conjectures might well consider what this paradigm shift may do to other geological conjectures. It may well cause a domino effect on current models in subjects as diverse as radiometric dating (which assumes pristine, unprocessed material from the deep mantle), planetary differentiation, seismology, volcanology, magnetic field dynamo theory, and even the origin of life. This model tinkers with temperatures, chemistry, the nature of the core and mantle, the timing of continents, and a host of geophysical processes affecting land and sea. Evolutionists had better revisit their assumptions about the early earth and what this does to their beliefs.
Now that mantle plumes and deep plate tectonics are out, who knows what will happen next? Perhaps Hamilton’s shallow plate tectonics theory will topple for other reasons. It seems to hinder large migrations of plates, such as the belief that India migrated from lower Africa, crashed into Asia and built the Himalayas. His choice of terms, “punctuated gradualism,” recalls Stephen Jay Gould’s punctuated equilibria, the “Alternative Earth” model in biology. It arose out of frustration with the lack of evidence for Darwinian gradualism, not because of positive evidence for the alternative. Gould replaced that “standard model” (neo-Darwinism) with – what? – a new model with even less empirical support, claiming, essentially, that evolution happens so fast it leaves no trace in the fossil record! Is Hamilton’s “Punctuated gradualism” a parallel in geology? It seems, at least, to nail the coffin shut on Lyell’s principle of uniformitarianism. Whatever happens next, we have just seen that major paradigm shifts are still possible in science. Kuhnians rejoice. Darwinians beware.