March 12 (UPI) — Hidden in the ancient rocks of Greenland, scientists have found the geochemical signatures of Earth’s early history, a time when the planet was one big ocean of magma.
At some point during Earth’s infancy, the molten ocean that covered the planet began to cool and crystalize, yielding Earth’s earliest rocks and landforms. This process set the stage for Earth’s tectonic evolution and the development of the planet’s atmosphere.
Unfortunately, this process isn’t well understood, as most all of the planet’s rocks older than 4 billion years have been subsumed by Earth’s interior and recycled.
In a breakthrough discovery, however, the authors of a new study — published Friday in the journal Science Advances — claim to have found remnants of primordial Earth’s molten oceans trapped in 3.6-billion-year-old rocks from southwestern Greenland.
“There are few opportunities to get geological constraints on the events in the first billion years of Earth’s history,” lead study author Helen Williams said in a press release.
“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 Williams, a geoscientist at Cambridge University in England.
Though they look a lot like any other basalt deposits, the outcropping of rocks that form Greenland’s Isua supracrustal belt are the oldest of their kind, and home to the earliest evidence of microbial life and plate tectonics.
The latest survey of Isua’s geological secrets revealed the presence of ancient crystals that formed as early Earth’s planet-wide 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,” said study co-author Hanika Rizo.
“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 Rizo, an associate professor of earth sciences at Carleton University in Canada.
Analysis of the iron isotope ratios found in the rocks suggests the Isua supracrustal belt was derived from a region of Earth’s interior formed by the crystallization of early Earth’s magma ocean.
Like an industrial smoothie mixer, Earth’s mantle is constantly turning over. Despite the non-stop convention, scientists suspect large pockets of ancient crystals at the mantle-core border have remained mostly undisturbed for billions of years.
Long ago, some of these ancient crystals were incorporated into the rocks that came to form the Isua supracrustal belt.
Isotopic analysis suggests these crystals slowly made their way from the deep mantle to Earth’s surface — crystalizing and melting, repeatedly, on their way up.
Eventually, this distillation process carried these ancient crystals into the upper mantle where they mixed with magma from other mantle layers. Later, the molten conglomerates became incorporated into Greenland’s crust.
The latest findings suggest Earth’s hotspot volcanoes, previously thought to have formed relatively recently, may actually be fueled by ancient mixtures of magma and crystal, not unlike the hybridized magma that forged the Isua supracrustal belt.
“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 co-author Oliver Shorttle, an earth scientist at Cambridge.