Mysteries of the Earth: Researchers predict how fast ancient magma ocean solidified

Date:
February 27, 2023
Source:
Florida State University
Summary:
Previous research estimated that it took hundreds of million years
for the ancient Earth's magma ocean to solidify, but new research
narrows these large uncertainties down to less than just a couple
of million years.


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FULL STORY ========================================================================== Early in the formation of Earth, an ocean of magma covered the planet's
surface and stretched thousands of miles deep into its core. The rate at
which that "magma ocean" cooled affected the formation of the distinct
layering within the Earth and the chemical makeup of those layers.


========================================================================== Previous research estimated that it took hundreds of million years
for that magma ocean to solidify, but new research from Florida State University published in Nature Communications narrows these large
uncertainties down to less than just a couple of million years.

"This magma ocean has been an important part of Earth's history, and this
study helps us answer some fundamental questions about the planet," said
Mainak Mookherjee, an associate professor of geology in the Department
of Earth, Ocean and Atmospheric Science.

When magma cools, it forms crystals. Where those crystals end up
depends on how viscous the magma is and the relative density of the
crystals. Crystals that are denser are likely to sink and thus change the composition of the remaining magma. The rate at which magma solidifies
depends on how viscous it is. Less viscous magma will lead to faster
cooling, whereas a magma ocean with thicker consistency will take a
longer time to cool.

Like this research, previous studies have used fundamental principles of physics and chemistry to simulate the high pressures and temperatures in
the Earth's deep interior. Scientists also use experiments to simulate
these extreme conditions. But these experiments are limited to lower
pressures, which exist at shallower depths within the Earth. They don't
fully capture the scenario that existed in the planet's early history,
where the magma ocean extended to depths where pressure is likely to be
three times higher than what experiments can reproduce.

To overcome those limitations, Mookherjee and collaborators ran their simulation for up to six months in the high-performance computing
facility at FSU as well as at a National Science Foundation computing
facility. This eliminated much of the statistical uncertainties in
previous work.

"Earth is a big planet, so at depth, pressure is likely to be very high,"
said Suraj Bajgain, a former post-doctoral researcher at FSU who is now
a visiting assistant professor at Lake Superior State University. "Even
if we know the viscosity of magma at the surface, that doesn't tell
us the viscosity hundreds of kilometers below it. Finding that is very challenging." The research also helps explain the chemical diversity
found within the Earth's lower mantle. Samples of lava -- the name for
magma after it breaks through the surface of the Earth -- from ridges
at the bottom of the ocean floor and volcanic islands like Hawaii and
Iceland crystallize into basaltic rock with similar appearances but
distinct chemical compositions, a situation that has long perplexed
Earth scientists.

"Why do they have distinct chemistry or chemical signals?" Mookherjee
said.

"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?" The starting point of chemical diversity in the
mantle can be successfully explained by a magma ocean in the Earth's
early history with low viscosity.

Less viscous magma led to the rapid separation of the crystals suspended
within it, a process often referred to as fractional crystallization. That created a mix of different chemistry within the magma, rather than a
uniform composition.

Doctoral student Aaron Wolfgang Ashley from FSU as well as Dipta Ghosh and Bijaya Karki from the Department of Geology and Geophysics at Louisiana
State University were co-authors of this paper.

This work was funded by the National Science Foundation.

* RELATED_TOPICS
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# Earth_Science # Volcanoes # Geology # Geochemistry
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o Geology_of_the_Capitol_Reef_area o Ichthyosaur
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========================================================================== Story Source: Materials provided by Florida_State_University. Original
written by Bill Wellock. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Suraj K. Bajgain, Aaron Wolfgang Ashley, Mainak Mookherjee, Dipta B.

Ghosh, Bijaya B. Karki. Insights into magma ocean dynamics from
the transport properties of basaltic melt. Nature Communications,
2022; 13 (1) DOI: 10.1038/s41467-022-35171-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/02/230227161352.htm

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