Ancient Moon experienced resurfacing after having been covered in magma

The lunar crust is composed of just one mineral, meaning a secondary resurfacing must have occurred.
By Laurel Kornfeld | Nov 24, 2017
Formed through a collision between proto-Earth and a Mars-sized object four billion years ago, Earth's Moon was covered with an ocean of magma before eventually cooling and being resurfaced.

Today, the lunar crust is composed of just one mineral--plagioclase--indicating a secondary event occurred after the magma cooled.

Scientists led by The University of Texas at Austin Jackson School of Geosciences created a simulation of the early molten Moon in a laboratory as a means of tracing the evolution of the current lunar surface.

In the simulation, the Moon's crust began to form when rocks floated to the top of the magma and started cooling.

"It's fascinating to me that there could be a body as big as the Moon that was completely molten," said research team leader Nick Dygert, now at the University of Tennessee in Knoxville.

"That we can run these simple experiments, in these tiny little capsules here on Earth and make first order predictions about how such a large body would have evolved is one of the really exciting things about mineral physics."

Most of the Moon's crust has a composition that is 98 percent plagioclase, as revealed by satellites, an unlikely composition that previous simulations could not explain.

This lack of crustal diversity has long confounded scientists, especially since the Earth, from which the Moon originated, has a rich diversity of minerals.

Dygert's laboratory research revealed that with a low viscosity or thickness, plagioclase would have floated to the top of the magma, but in doing so, it would have trapped other minerals, producing a crust that would not be pure plagioclase.

A second resurfacing of the Moon's crust in which hot, pure plagioclase replaced an older, more mixed surface, had to have occurred to explain the composition of today's lunar crust, he noted.

That resurfacing could also have been the results of asteroid impacts, which eroded the Moon's earlier, mixed crust.

The phenomenon is known as "crustal overturn," and it may occur on many planets and moons.

A paper detailing the findings has been published in the Journal ofGeophysical Research: Planets.



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