Light matter in the core of the Earth: its identity, quantity and temperature using tricritical phenomena

TL;DR

This study uses tricritical phenomena theory combined with seismic and melting data to determine the identity, quantity, and temperature of light elements in Earth's core, resolving longstanding uncertainties.

Contribution

It introduces a novel application of tricritical phenomena theory to analyze Earth's core composition and temperature, providing new estimates for light element content and identity.

Findings

Light element amount is about 2.5 mole%.

The light matter is identified as MgSiO3.

Solid and liquid iron densities at melting are determined.

Abstract

Light elements in the iron-rich core of the Earth are important indicators for the evolution of our planet. Their amount and distribution, and the temperature in the core, are essential for understanding how the core and the mantle interact and for modelling the geodynamo which generates the planetary magnetic field. However, there is a longstanding controversy surrounding the identity and quantity of the light elements. Here, the theory of tricritical phenomena is employed as a precise theoretical framework to study solidification at the high pressures and temperatures where both experimental and numerical methods are complicated to implement and have large uncertainties in their results. Combining the theory with the most reliable iron melting data and the Preliminary Reference Earth Model (PREM) seismic data, one obtains the solidification temperature at the inner core boundary (ICB) for both pure iron and for the alloy of iron and light elements in the actual core melt. One also finds a value of about 2.5 mole% for the amount of light matter. In addition, the density of both solid and liquid pure iron at its melting temperature is found. This allows one to obtain the density of the light matter and thus to identify it to be MgSiO3.