In early Earth history, silicate melts would have greatly affected mantle dynamics due to violent collisions that resulted in large-scale melting of the mantle, i.e. magma-ocean stage. If such a magma ocean existed, dense metal melt droplets would likely settle through the silicate-rich molten mantle. The viscosity of such a magma ocean or its constituent silicate melt is crucial in determining the thermal and chemical evolution of the planet.
Florida State University scientists reported the results of first-principle molecular dynamics simulations of basalt melt. This research reduces the significant uncertainties to less than a few million years, compared to previous estimates that the magma ocean took hundreds of millions of years to solidify.
Mainak Mookherjee, an associate professor of geology in the Department of Earth, Ocean, and Atmospheric Science, said: “This magma ocean has been an important part of Earth’s history, and this study helps us answer some fundamental questions about the planet.”
Similar to this discovery, previous studies have simulated the high pressures and temperatures in the Earth’s deep interior using fundamental physics and chemistry principles. To simulate these harsh conditions, scientists also use experiments.
However, these experiments are limited to lower pressures that exist at shallower depths in the Earth. They can’t accurately describe the scenario that prevailed during the planet’s early history when the magma ocean expanded to depths where pressures are probably three times greater than what experiments can replicate.
To get around those limitations, Mookherjee and colleagues ran their simulation in a high-performance computing facility at FSU and one owned by the National Science Foundation for up to six months. This significantly reduced the statistical uncertainties we saw in previous work.
The study contributes to understanding the chemical diversity present in Earth’s lower mantle. It has long baffled earth scientists why samples of lava, the term for magma when it erupts through the Earth’s surface, from volcanic islands such as Hawaii and Iceland and ridges on the ocean floor split into basalt rock with similar appearance but different chemical compositions.
Mookherjee said, “Why do they have different chemistry or chemical signals? Since the magma originates from below the Earth’s surface, this means that the source of the magma has chemical diversity there. How did that chemical diversity begin in the first place and how has it survived geological time?”
A low-viscosity magma ocean in Earth’s early history may successfully explain the origin of chemical diversity in the mantle. The crystals trapped in less fluid magma quickly separated, a process known as fractional crystallization. Instead of the magma having a consistent composition, it resulted in a mixture of varied chemistry.
- Bajgain, SK, Ashley, AW, Mookherjee, M. et al. Insights into magma-ocean dynamics through the transport properties of basalt melt. Nat Commun 13, 7590 (2022). DOI: 10.1038/s41467-022-35171-y