Several billion years ago, it is assumed that the Earth was coiled in a vast ocean of magma. Due to plate tectonics, we have little evidence left of what this “young version” of our planet looked like. In Greenland, researchers have nevertheless been able to isolate rocks testifying to this ardent past.
Shortly after its formation, the Earth was a real “orange lollipop” completely covered with an ocean of molten magma. And for good reason, our world was regularly attacked from all sides, wiping the “slaps” of huge objects, including the one responsible for the formation of the Moon. The heat from these impacts therefore inevitably delayed its cooling process. According to models, this is a fairly common stage in planetary evolution.
Then, after a while, things calmed down, the impacts became scarce and the temperatures dropped. The plate tectonics process eventually took over, and evidence from those ancient times was drawn into the Earth’s interior for recycling. However, it seems that some of these relics have survived.
The chemical signatures isolated in basaltic rocks of Greenland old from 3.7 billion years indeed support the theory that our planet was once coiled in magma.
In Greenland, the Isua greenstone belt, also known as the Isua supracrustal belt, rivals the Jack Hills, an Australian chain of hills home to some of the oldest minerals of terrestrial origin.
“There is little possibility of obtaining geological constraints on the events of the first billion years of Earth’s history.“, Recalls Dr. Helen Williams of the University of Cambridge. “It is amazing that we can even hold these rocks in our hands and even more so get so many details about the beginnings of the history of our planet“.
In the review Scientific progress, Williams and his team explain having analyzed crystals in Isua rocks, whose chemistry (high levels of heavy iron isotopes) would indicate that they formed at at least 700 kilometers below the surface of the Earth. Lighter iron isotopes generally occur in younger balsamic rocks.
These conclusions were only possible thanks to recent advances in the understanding of how the isotopic ratios of iron vary with the temperatures and pressures under which the crystals containing them form.
Melted reconstructions of old materials
Concretely, these crystals would then have taken a path towards the surface to finally form these rocks of Greenland, partially melting and recrystallizing several times during their journey without completely erasing their previous transformations.
“Old rocks, like those in Greenland, are melted reconstructions of ancient materials“, Summarizes Catherine McCammon, the University of Bayreuth in Germany.
Although this is the first evidence of the existence of a magmatic ocean at the beginning of Earth’s history, the team is convinced that several of these oceans existed before it. However, it will still take a lot of work and patience to isolate and analyze other “surviving” geosignatures.