Large density jumps in numerical simulations of solid Earth dynamics can cause numerical oscillations. An effective method to prevent these at a free surface already exists. Here this is tested for compositional layers deeper in the mantle. The stabilisation method works effectively if density gradients due purely to compositional gradients are used but produces severe artefacts if total density is used.

The mantle thermal conductivity's dependencies on temperature, pressure, and composition are often suppressed in numerical models. We examine the effect of these dependencies on the long-term evolution of lower-mantle thermochemical structure. We propose that depth-dependent conductivities derived from mantle minerals, along with moderate temperature and compositional correction, emulate the Earth's mean lowermost-mantle conductivity values and produce a stable two-pile configuration.

The lower mantle extends from 660–2890 km depth, making up > 50 % of the Earth’s volume. Its composition and structure, however, remain poorly understood. In this study, we investigate several hypotheses with computer simulations of mantle convection that include different materials: recycled, dense rocks and ancient, strong rocks. We propose a new integrated style of mantle convection including piles, blobs, and streaks that agrees with various observations of the deep Earth.

We use numerical models to investigate the thermo-chemical evolution of a solid mantle during a magma ocean stage. When applied to the Earth, our study shows that the solid mantle and a magma ocean tend toward chemical equilibration before crystallisation of this magma ocean. Our findings suggest that a very strong chemical stratification of the solid mantle is unlikely to occur (as predicted by previous studies), which may explain why the Earth’s mantle is rather homogeneous in composition.