How fast did the ancient magma ocean solidify?

This study helps us answer some fundamental questions about the planet.

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In the Earth’s early history, silicate melts would have strongly influenced mantle dynamics because of violent collisions that resulted in large-scale melting of the mantle, i.e., magma ocean stage. If such a magma ocean existed, dense metallic 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 for determining the thermal and chemical evolution of the planet.

Scientists from Florida State University reported the results of first-principles molecular dynamics simulations of basaltic melt. This research reduces the significant uncertainties to less than a few million years, compared to previous estimates that the magma ocean required 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, earlier studies have simulated the high pressures and temperatures in the Earth’s deep interior using basic physics and chemistry principles. To simulate these harsh conditions, scientists also use experiments.

These experiments, however, are restricted to lower pressures that exist at shallower depths in the Earth. They fall short of accurately describing the scenario that prevailed during the planet’s early history when the magma ocean spread to depths where pressure is probably three times greater than what experiments can replicate.

To overcome those restrictions, Mookherjee and colleagues performed 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 seen in earlier work.

The study contributes to the understanding of the chemical diversity present in the lower mantle of the Earth. It has long baffled Earth scientists why samples of lava, the term for magma when it bursts through the surface of the Earth, from volcanic islands like Hawaii and Iceland and ridges at the bottom of the ocean divide into basaltic rock with similar appearances but different chemical compositions.

Mookherjee said“Why do they have distinct chemistry or chemical signals? Since the magma originates from underneath the Earth’s surface, that means the source of the magma there has chemical diversity. How did that chemical diversity begin in the first place, and how has it survived over geological time?”

A low-viscosity magma ocean in the Earth’s early history can successfully account for the origin of chemical diversity in the mantle. The crystals trapped within less fluid magma separated quickly, a process known as fractional crystallization. Instead of the magma having a consistent composition, this resulted in a mixture of varied chemistry.

Journal Reference:

  1. Bajgain, S.K., Ashley, A.W., Mookherjee, M. et al. Insights into magma ocean dynamics from the transport properties of basaltic melt. Nat Commun 13, 7590 (2022). DOI: 10.1038/s41467-022-35171-y

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