Hidden pressure-stabilized lead reservoirs in Earth’s mantle

Why hidden lead deep underground matters

Lead locked away far beneath our feet turns out to hold clues to how our planet formed and evolved. For decades, scientists have wrestled with a puzzle: the lead we can sample from Earth’s rocks looks more “radiogenic” than expected, as if a large amount of original, non-radiogenic lead has gone missing. This paper explores the idea that the missing lead is not in the core, as often assumed, but trapped in special lead–sulfur minerals that become stable only under the immense pressures of Earth’s deep mantle.

A long-standing mystery about Earth’s lead

Geochemists use different forms of lead, created by the slow radioactive decay of uranium and thorium, as a kind of clock and tracer for Earth’s history. When they compare the lead found in accessible mantle rocks and continental crust with primitive meteorites, the accessible Earth seems too enriched in radiogenic lead. This “missing lead paradox” suggests that a large reservoir of old, non-radiogenic lead exists somewhere out of reach. Previous ideas put this reservoir mainly in the metallic core, but experiments and partitioning calculations indicate the core cannot hide enough lead on its own. That points to an additional, still-hidden storehouse inside the rocky part of the planet.

New lead–sulfur minerals under crushing pressure

The authors tackled this problem by using powerful computer methods to search for all the stable ways that lead and sulfur atoms can arrange themselves under the extreme pressures found from the surface down to the core–mantle boundary. They confirmed that galena (PbS), a common ore mineral at the surface, remains stable across this vast pressure range and passes through several denser crystal structures as pressure increases. More intriguingly, they identified two additional compounds, PbS2 and PbS3, that become stable only at high pressures and contain unusual chains and clusters of sulfur atoms. Calculations of their vibrational properties show that these phases are dynamically stable, and their electronic structures reveal that electrons are strongly shared within the sulfur units, helping to stabilize these minerals when squeezed deep in the mantle.

How these minerals behave inside a hot planet

To test whether these phases could actually exist in Earth, the team computed how they respond not only to pressure but also to high temperature, constructing phase diagrams and estimating melting points. PbS turns out to be extremely refractory: even near core–mantle boundary conditions it remains solid, with no sign of atomic diffusion, meaning that once it crystallizes it can endure for billions of years. PbS2 is also relatively hard to melt and can stay crystalline in the upper mantle and lower crust. PbS3, by contrast, has melting temperatures that lie just below or around estimated mantle temperatures, so it is likely to occur partly as a melt at depth. Together, these contrasting behaviors set the stage for a system that both locks lead away and occasionally leaks some of it back toward the surface.

A deep storehouse and a slow leak back to the surface

The authors propose a planetary story that starts with Earth’s early magma ocean and core formation. In that fiery beginning, lead tended to join sulfur-rich liquids, some of which may have carried a portion of lead into the core. But their calculations show that a large fraction of lead could instead have been trapped in dense PbS crystals that settled in the deep mantle, safely separated from uranium and thorium and thus preserving their ancient isotopic character. Later in Earth’s history, subduction carried extra sulfur into the mantle, creating sulfur-rich pockets where PbS could react to form PbS2 and especially the lower-melting PbS3. As PbS3 melts and is moved upward by mantle flow, it eventually breaks down at shallower depths, releasing small amounts of unradiogenic lead back into regions sampled by volcanic rocks. This slow “leak” helps explain rare observations of unusually unradiogenic lead in some mantle samples.

What this means for our picture of Earth

In plain terms, the study shows that the missing lead paradox can be understood without invoking an exotic core-only reservoir. Instead, Earth may hide much of its original lead in stubborn, pressure-stabilized lead–sulfur minerals buried deep in the mantle, while sulfur-rich reactions create a limited pathway for some of that ancient lead to return to the surface over time. This work links the planet’s redox and sulfur cycles to the long-term evolution of its lead isotopes, and suggests that similar high-pressure sulfide reservoirs may quietly shape the chemical histories of other rocky worlds as well.

Citation: Liu, S., Guo, M., Yu, S. et al. Hidden pressure-stabilized lead reservoirs in Earth’s mantle. Nat Commun 17, 2913 (2026). https://doi.org/10.1038/s41467-026-69772-8

Keywords: lead isotopes, Earth mantle, sulfide minerals, planetary differentiation, deep reservoirs