A study published in Earth and Planetary Science Letters challenges a widely held assumption about the thermal state of Earth’s interior before the supercontinent Pangea began to fragment around 200 million years ago. By measuring the thickness of the oldest oceanic crust along the Atlantic and Indian Ocean margins, the researchers found that mantle temperatures at the time of breakup were far lower than the “continental insulation” model predicts. The result forces a rethink of how supercontinents interact with the deep Earth and what drives the volcanic activity that accompanies their breakup.
The Thermal Blanket That May Not Have Existed
For decades, geoscientists have treated Pangea like a planetary lid. The idea is straightforward: a massive continent sitting in one place for tens of millions of years traps heat rising from the mantle below, gradually warming the upper mantle until rifting releases that stored energy as thick volcanic crust. A 2012 study in Nature Geoscience built a strong case for this view, reporting that Atlantic mid-ocean ridge basalt compositions near rifted continental margins recorded upper-mantle temperatures up to roughly 150 degrees Celsius above the present-day average, with that thermal signal persisting for roughly 60 to 70 million years after rifting. Pacific samples far from any continent did not show the same elevated signal, which seemed to confirm that continental insulation was the driver.
A separate compilation of global marine seismic refraction data, published in Nature Geoscience in 2017, reinforced the picture from a different angle. That study reported that mid-Jurassic crust dating to roughly 170 million years ago was about 1.7 km thicker on average than crust forming at mid-ocean ridges today. Because hotter mantle produces thicker crust when it wells up beneath a spreading ridge, the thickness gap pointed to a substantially warmer interior during and just after Pangea’s breakup. Together, these two lines of evidence became the standard framework: Pangea insulated the mantle, the mantle got hotter, and the proof was written in the thickness and chemistry of the ocean floor.
New Measurements Tell a Different Story
The 2026 study takes a different approach. Instead of compiling global averages of crustal thickness across all ocean-floor ages, the researchers focused specifically on the first-formed oceanic crust near the landward limit of oceanic crust along Atlantic and Indian rifted margins. This measurement captures the very first ocean floor created as Pangea tore apart, making it a direct thermometer for mantle conditions at the moment of breakup rather than millions of years later. The team drew on lithospheric thickness models derived from the Priestley (McKenzie) dataset archived in PANGAEA and used seafloor age grids to pin down when each strip of crust formed.
What they found clashes with the insulation narrative. According to the study, crust produced just after breakup was only slightly thicker than the present-day average of roughly 6.7 km. Rather than the uniform hot blanket beneath the entire supercontinent that earlier models predicted, the data point to mantle potential temperature anomalies that were modestly elevated in some regions and near-normal or even cooler in others. This contrasts with the 1.7 km average excess thickness reported in the 2017 global compilation, which blended crust of many ages and distances from continental margins into a single number.
Why the Numbers Disagree
The tension between the two sets of findings is real, but it does not necessarily mean one is wrong. The 2017 study averaged crustal thickness across entire ocean basins and all Jurassic-age crust, including sections that formed millions of years after initial rifting. By that point, mantle plumes, small-scale convection, and other regional heat sources could have thickened the crust independently of any continental insulation effect. The 2026 paper, by contrast, isolates the earliest crust at the landward oceanic edge along rifted margins, which records conditions before those secondary processes had time to act. If the mantle directly beneath Pangea was only mildly warm at the start of breakup, the thicker crust observed later in the Jurassic may reflect localized plume activity or changes in plate-spreading rates rather than a continent-wide thermal buildup.
The detailed thickness distribution in the new dataset supports this view. As summarized in the crustal groupings, some rift segments produced crust close to the modern average, while others yielded only modestly thicker packages, inconsistent with a strongly overheated mantle everywhere beneath the former supercontinent. The 2012 geochemical evidence from Atlantic basalts also deserves a second look through this lens. Those elevated temperature signals came from rocks near rifted margins, where the transition from thick continental lithosphere to thin oceanic lithosphere creates complex flow patterns in the mantle. Edge-driven convection and small plumes channeled along the base of thinning continental plates could produce locally hot basalts without requiring the entire sub-Pangean mantle to be uniformly superheated.
What This Means for Earth’s Cooling History
Earth has been losing heat since its formation, and the rate at which that heat escapes through the mantle and crust is central to models of the planet’s thermal evolution. Continental insulation has long been invoked as a mechanism that could temporarily slow that cooling by bottling up heat beneath supercontinents, only to release it in bursts of magmatism during breakup. If the mantle beneath Pangea was not dramatically hotter at the onset of rifting, as the new crustal measurements indicate, then the role of supercontinents in modulating Earth’s heat loss may be weaker and more regionally variable than previously assumed. Instead of acting as a simple thermal blanket, a supercontinent might redirect mantle flow, concentrating heat beneath particular rift zones while leaving other areas relatively unaffected.
This reinterpretation has knock-on effects for how geoscientists read the rock record. Large igneous provinces and thick volcanic passive margins have often been taken as signatures of global mantle overheating linked to supercontinent breakup. The new work suggests that such features may instead reflect a complex interplay of regional processes, including mantle plumes, lithospheric structure, and variable extension rates, superimposed on a mantle that was only modestly warmer than today. That perspective encourages more nuanced reconstructions of past mantle temperatures, emphasizing local context over global averages.
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*This article was researched with the help of AI, with human editors creating the final content.
