An ocean of magma covered the planet's surface and extended thousands of miles deep into its core early in its formation.
The rate at which that "magma ocean" cooled influenced the formation of distinct layers within the Earth as well as the chemical composition of those layers.
Previous research estimated that the magma ocean solidified over hundreds of millions of years, but new research from Florida State University published in Nature Communications reduces these large uncertainties to less than a couple of million years.
Mysteries of the Earth
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"This magma ocean has been an important part of Earth's history," said Mainak Mookherjee, an associate professor of geology in the Department of Earth, Ocean, and Atmospheric Science, as per ScienceDaily.
When magma cools, crystals form. The location of those crystals is determined by the viscosity of the magma and the relative density of the crystals.
Denser crystals are more likely to sink, changing the composition of the remaining magma.
The rate at which magma solidifies is determined by its viscosity.
A magma ocean with less viscous consistency will cool faster, whereas a magma ocean with a thicker consistency will take longer to cool.
Previous studies, like this one, used fundamental physics and chemistry principles to simulate the high pressures and temperatures in the Earth's deep interior.
Experiments are also used by scientists to simulate these extreme conditions.
These experiments, however, are limited to lower pressures found at shallower depths within the Earth.
They don't fully capture the scenario that existed in the planet's early history when the magma ocean extended to depths where pressure was likely three times greater than what experiments can reproduce.
To overcome these constraints, Mookherjee and his colleagues ran their simulation for up to six months in FSU's high-performance computing facility and a National Science Foundation computing facility.
This eliminated a large portion of the statistical uncertainty in previous work.
"Because Earth is a big planet, pressure at depth is likely to be very high," said Suraj Bajgain, a former FSU postdoctoral researcher who is now a visiting assistant professor at Lake Superior State University.
Even if the researchers knew the viscosity of magma at the surface, theu don't know the viscosity hundreds of kilometers beneath the surface and finding that is extremely difficult.
The study also contributed to understanding the chemical diversity found in the Earth's lower mantle.
Lava samples from ridges at the bottom of the ocean floor and volcanic islands, such as Hawaii and Iceland crystallize into basaltic rock with similar appearances but distinct chemical compositions, a situation that has long been observed.
The origin of chemical diversity in the mantle can be successfully explained by a low-viscosity magma ocean in Earth's early history.
Less viscous magma caused the crystals suspended within it to separate more quickly, a process known as fractional crystallization.
Instead of a uniform composition, this resulted in a mix of different chemistry within the magma.
Magma oceans appear to be a common result of large rocky body formation processes.
Small planetesimals and embryos can form in the protoplanetary disc on very short time scales, incorporating significant amounts of short-lived radionuclides like 26Al and 60Fe that can generate enough heat to partially melt many of these objects, as per The Royal Society.
According to models, the asteroid 4 Vesta, which is the source of the howardite-eucrite-diogenite (HED) meteorites, went through a magma ocean stage as a result of such brief heating.
Many iron meteorites, which are most likely the remains of differentiated planetesimals, have ages of only about 1 Myr after the formation of the Solar System, indicating very early, short-lived magma oceans.
Larger objects, such as the Earth, take so long to build that short-lived radionuclides cannot provide enough heating to melt them.
Significant heating can result from accretionary impacts and gravitational segregation of metallic iron into the planet's core for these larger, later-assembling bodies.
Giant impacts appear to be common in N-body simulations of rocky planet formation, and they are likely to cause widespread melting, which can lead to silicate and metal differentiation.
