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Scientists have found evidence in ancient rocks from southern Greenland that indicates much of the Earth was once entirely molten.
Very little is known about what the Earth looked like during the Hadean Eon, which is characterized by the planet’s initial formation, the stabilization of its core and crust, and formation of its early atmosphere.
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In a study published Friday in the journal Science Advances, geochemists working together from across the globe reported that their analysis of billions-of-years-old rocks from the Isua supracrustal belt — which contains the oldest known rocks on the planet — found chemical traces of a magma ocean.
Their samples of 3.7-billion-year-old basalt rocks were found to have high levels of heavy iron isotopes, which were measured using chromatography and mass spectroscopy.
The researchers identified hafnium and neodymium isotopes, as well as rare tungsten isotopes stemming from an “ancient parent isotope” that only existed in the Earth’s first 45 million years, according to LiveScience.
“It was a combination of some new chemical analyses we did and the previously published data that flagged to us that the Isua rocks might contain traces of ancient material. The hafnium and neodymium isotopes were really tantalizing, because those isotope systems are very hard to modify – so we had to look at their chemistry in more detail,” the study’s co-author and Carleton University associate professor Dr. Hanika Rizo explained.
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The iron isotopes confirmed to the team that the Isua rocks had been made up of parts of the Earth’s interior that formed 4.5 billion years ago as a consequence of magma ocean crystallization.
They reported that crystal residues had melted and mixed with other molten rock upon moving to the Earth’s upper mantle, carrying the isotopes along with rock from both the lower and upper mantle.
How they emerged on the surface is less clear, but a Cambridge University release notes that catastrophic collisions during the formation of the Earth and Moon would have generated enough energy to melt the planet’s interior — which would eventually cool and crystalize — with the isotopes migrating by crystalizing and re-melting.
Since then, tectonic shifts have “recycled” almost all rocks older than four billion years.
“Finding the geological evidence for the Earth’s former molten state is extremely difficult. This is because magma ocean crystallisation events would have taken place over 4 billion years ago, and much of the geological record from that period of Earth’s history has been lost since then,” lead author Helen Williams, a professor of geochemistry at Cambridge, told Fox News on Saturday.
Additionally, because much of the deep Earth is inaccessible, Williams and the team had to rely on nature to assist their research, though she noted that the chemistry of volcanic rocks was vital to their conclusions.
“Our results provide tantalizing evidence for the presence of deep magma ocean crystals formed from a time when the Earth was almost entirely molten,” she said.
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“Although the results of our research are very exciting, they also pose further questions. What processes were responsible for the melting events that produced the Isua volcanic rocks? Were all ancient volcanic rocks derived from regions of the Earth’s mantle containing residual crystals formed during the cooling of a magma ocean? Is any of this material still present in the interior of the modern Earth and if so, can it explain the unique chemistry of magmas erupted in ‘hot spots’ like Hawaii and Iceland?”
“Clearly, much more remains to be discovered,” she said.
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