Rocks collected in Greenland may contain traces of an ancient magma ocean that bubbled over much of Earth’s surface shortly after the planet’s birth, a new study finds.
Scientists collected the rocks from the Isua Supracrustal Belt, a region in the southwest Greenland where the exposed rocks are between 3.7 billion and 3.8 billion years old; the belt contains the oldest known stones Soil, which remain relatively undisturbed by it plate tectonics, heat and chemical changes, according to Science Magazine
The chemical traces of the early magma oceans are even older than the rocks themselves, which date back to about 4.5 billion years ago, when an object the size of Mars smashed into Earth and knocked off a huge chunk of rock that later became the moon, according to the new study.
When celestial objects the size of Earth and Mars collide, “the near-widespread melting of the entire planet is an inevitable consequence,” lead author Helen Williams, a professor of geochemistry at Cambridge University, said. Live Science. And as that molten rock cooled and crystallized, the Earth gradually began to resemble the blue marble we know today, she said.
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But while most scientists accept the molten Earth theory, “a major challenge is that it is very difficult to find … geological evidence for anything that happened so early in our history,” Williams said. The new study, published March 12 in the journal Science Advances, shows that rocks in the Isua Belt still bear chemical “fingerprints” left by this primordial cooling process.
Williams began looking for these fingerprints after she and her co-author Hanika Rizo, associate professor at Carleton University in Canada, met at a fall meeting of the American Geophysical Union (AGU), an annual event held in pre-pandemic times for decades. from thousands of scientists from around the world.
Rizo had previously taken rock samples from the Isua supracrustal belt and written about it in a 2011 study published in the journal Earth and Planetary Science LettersIn the article, she noted that the rocks bore certain chemical characteristics, namely unique isotopes or chemical elements with varying numbers of neutrons. Williams later read the report, and these chemical signatures piqued her interest.
Her paper does not provide direct geological evidence for the magma ocean. But so many of the chemical tracers she discusses … really point in that general direction, Williams said. If they studied the samples further, Williams thought, they could discover a snapshot of it Soil‘s melted past. So when she saw Rizo across the street from the sprawling AGU conference room, “I actually ran up to her because I really wanted to talk … about the possibility of working together,” Williams said.
To initiate their collaboration, the scientists went to the lab. They selected a subset of volcanic rocks of the Isua samples, picking only the most pristine, in terms of how much wear and tear they underwent after erupting to the surface and exposed to the elements. Then they sawed off the exposed surfaces of the rocks, sanded them, ground them into a fine powder and dissolved the powder in strong acids.
“By the time you’re done, it’s pretty unbelievable that something that was a really hard, dense rock in your hand is now actually a small bottle of liquid in your lab,” Williams said. Processing the rocks in this way allowed the team to examine isotopes or chemical elements with varying numbers of neutrons in the samples.
Specifically, the team was looking for isotopes that would have formed when the magma oceans crystallized. Models suggest that some remnants of these crystals are trapped in the lower mantle, close to the core of the earth, and would have survived for billions of years. Over time, they would migrate through the lower mantle to the upper mantle, carrying the “isotopic fingerprints” of the magma ocean with them, Williams said.
These include fingerprints hafnium and neodymium isotopes, which form when their parent isotopes decay; this degradation occurs in a specific pattern when the parent isotopes are placed under extremely high pressure, such as those in the depths of the lower mantle, Williams said. The team found these unique isotopes in the Isua samples, along with a rare form of the element tungstenThese unusual tungsten isotopes, known as a “tungsten anomaly,” come from an ancient parent isotope that existed only in the first 45 million years of Earth’s history, Williams said.
As these crystal residues moved up from the lower to the upper mantle, they melted and mixed with other molten rocks, creating a marble effect. So when that mixed rock broke through the crust, he bore the isotope fingerprints along with the rock of both the upper and lower mantles; this applied to the Isua samples. There are several theories as to how and why the crystals migrated upward through the Earth’s layers, one of which is that the crystals repeatedly melted and recrystallized, becoming more concentrated as they moved upward, Williams said.
After uncovering the chemical traces of magma oceans, “the question I have is whether other ancient rocks on Earth have retained the same signatures,” Williams said. She and her team are beginning to hunt for these signatures in locations around the world, in locations with extremely ancient rocks, and in modern hot spots for volcanic activity, such as Hawai’i and Iceland.
“A lot of evidence … suggests that these modern hotspots are derived from the melting of material really deep within the Earth, perhaps even coming from close to the boundary between Earth’s mantle and its core,” Williams said. That means chemical traces from the magma ocean could also lurk in these hot spots, although we’re not sure yet, she said.
Originally published on Live Science.