The Heresy of a Growing World

From the Lesson

THE HERESY OF A GROWING WORLD — SAMUEL WARREN CAREY & THE BETRAYAL OF PLATE TECTONICS

There is a name that every geology student learns in passing and then promptly forgets — or is encouraged to forget. That name is Samuel Warren Carey, and the story of his intellectual journey is one of the most quietly devastating tales in the history of science. For it was Carey who did more than almost anyone to assemble continental drift into the coherent framework that became plate tectonics — and it was Carey who, having seen what the establishment did with his work, spent the second half of his career trying to correct what he regarded as a catastrophic error.

THE ARCHITECT WHO DISOWNED HIS BUILDING

In the 1950s and 1960s, Samuel Warren Carey was a titan of structural geology. Working from the University of Tasmania, he convened the landmark 1956 Continental Drift Symposium in Hobart — one of the pivotal events that shifted the geological establishment from dismissing Alfred Wegener's drift hypothesis to taking it seriously. Carey's meticulous work on oroclines — the bending of mountain chains — provided some of the most compelling geometric evidence that the continents had once been joined. His analysis of the Bolivian Orocline in the Andes and the Alaska Orocline demonstrated that these mountain bends could only be explained by the curvature of continental margins on a smaller globe — a detail conveniently omitted from the textbook version of his work.

Carey's 1958 monograph, "The Tectonic Approach to Continental Drift," published by the University of Tasmania, laid out the geometric framework that later workers such as J. Tuzo Wilson, Dan McKenzie, and W. Jason Morgan would develop into plate tectonics proper. His concept of sphenochasm — a triangular gap that opens in the Earth's crust during rifting — became a fundamental tool of structural analysis. His description of the opening of the Bay of Biscay as a sphenochasm remains a textbook example taught to this day (Carey, S.W., "The Tectonic Approach to Continental Drift," Geology Department, University of Tasmania, 1958, pp. 177-355).

But even as the scientific community built its grand unified theory of plate tectonics upon foundations that Carey had helped lay, the man himself was growing deeply uneasy. The problem was subduction.

THE SUBDUCTION PROBLEM

Plate tectonics requires a closed system. If new crust is being created at mid-ocean ridges — and the seafloor magnetic striping discovered by Vine and Matthews in 1963 (Vine, F.J. & Matthews, D.H., "Magnetic Anomalies over Oceanic Ridges," Nature, 199, pp. 947-949) proved this beyond doubt — then an equal amount of crust must be destroyed somewhere else, or the Earth would be growing. The proposed mechanism for this destruction is subduction: oceanic plates diving beneath continental plates and being recycled into the mantle.

Carey looked at this proposition with the cold eye of a structural geologist and found it wanting. The geometry didn't work. When he reconstructed the continents on a globe at approximately 55% of Earth's current radius — roughly 3,500 kilometers versus today's 6,371 — the continents fit together perfectly. Not just across the Atlantic, as Wegener had shown, but everywhere. All the continents, on a smaller globe, tessellated like the panels of a football. No gaps. No overlaps. No missing pieces.

On the current-sized Earth, plate tectonics requires vast "subduction zones" where ocean floor is consumed. But the physical evidence for this consumption is remarkably thin. The seismic data shows plates descending, yes — but descending into what? The lower mantle shows no graveyard of recycled oceanic crust. The chemical signature that should mark billions of years of massive crustal recycling — the isotopic fingerprint of re-melted ocean floor — is largely absent from mantle-derived magmas.

THE MASS BALANCE PROBLEM — THE NUMBERS THAT DON'T ADD UP

The mass balance arithmetic of plate tectonics has never been rigorously closed. The issue is quantitative: the total area of new oceanic crust produced at mid-ocean ridges over geological time must equal the total area consumed at subduction zones, or the Earth's surface area is changing.