The research is providing new insight into a critical time during the formation of the Earth, when a deep sea of magma covered its surface and extended hundreds of kilometers into its interior.
“There are few opportunities to get geological constraints on the events in the first billion years of Earth’s history. It’s astonishing that we can even hold these rocks in our hands – let alone get so much detail about the early history of our planet,” said study lead author Dr. Helen Williams.
The gradual cooling and crystallization of the “magma ocean” produced the chemistry and x structure of the planet’s interior.
The rocks, recovered from Greenland’s Isua supracrustal belt, date back 3.6 billion years. The chemical remnants contained in them provide a window into a time when the planet started to solidify.
According to the experts, the findings suggest that other rocks on Earth’s surface may also preserve evidence of ancient magma oceans.
“The geochemical signals we report in the Greenland rocks bear similarities to rocks erupted from hotspot volcanoes like Hawaii – something we are interested in is whether they might also be tapping into the depths and accessing regions of the interior usually beyond our reach,” said study co-author Dr. Oliver Shorttle.
The team conducted a forensic chemical analysis on the rocks and identified residues of some of the crystals left behind as the ancient magma ocean cooled.
“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,” said study co-author Dr. Hanika Rizo.
Most of the rocks in Earth’s interior that formed from magma ocean crystallization have been mixed up by convection in the mantle, but scientists believe that some crystal graveyards may have remained undisturbed for billions of years in isolated areas deep at the mantle-core boundary
“Those samples with the iron fingerprint also have a tungsten anomaly – a signature of Earth’s formation – which makes us think that their origin can be traced back to these primeval crystals,” said Dr. Williams.
The researchers plan to expand their search for clues in ancient rocks to gain a better understanding of Earth’s early magma ocean.
“We’ve been able to unpick what one part of our planet’s interior was doing billions of years ago, but to fill in the picture further we must keep searching for more chemical clues in ancient rocks,” said study co-author Dr. Simon Matthews from the University of Iceland.
The study is published in the journal Science Advances.