Before Earth, there was a “proto-Earth”, a primitive piece of rock that formed four and a half billion years ago. It was drastically different from Earth as we know it today, spreading lava and rock across its barren surface and bubbling with potential.
This molten phase did not last long. When it was less than 100 million years old, what scientists believe was a Mars-sized object slammed into space and violently severed what it had grown into. The collision was so catastrophic that it not only blew up the debris that would later become our Moon, but also changed the composition of the planet forever. All traces of mind Earth were thought to have been lost or erased.
So far it is. In a new study published in the journal Natural geosciencesA team of MIT researchers claims to have discovered the first distinct remains of Earth’s primordial mind material, providing a tangible link to this lost era of our planet’s evolution. The breakthrough, the authors say, is a unique chemical “anomaly” found in ancient and deep-seated rock samples.
“This may be the first direct evidence that we have preserved the materials of Earth’s mind,” lead author Nicole Nie, an associate professor of Earth and planetary sciences at MIT, said in a statement about the work. “We’re seeing a piece of a very ancient Earth, even before the giant impact. This is remarkable because we would expect this very early signature to be slowly erased during Earth’s evolution.”
The key to their discovery came not from the underground, but from the sky: meteorites. From 2023 Nie’s team analyzed the chemical composition of meteorites around the world, each space rock serving as a time capsule from a different point in the Solar System’s 4.6 billion-year history. The samples of different ages together form a sort of timeline of the evolution of our star system.
An interesting development occurred when the scientists compared the composition of the meteorite samples with Earth samples. In their analysis, the meteorites showed what the scientists called a “potassium isotope anomaly,” or in short, an unusual ratio of different potassium isotopes.
The dominant isotopes of potassium on Earth today are potassium-39 and potassium-41, with another isotope, potassium-40, accounting for almost a fraction. But in the meteorites, the researchers found that the potassium isotope balance of the space rock did not match the Earth samples, suggesting that any other rocks with the same potassium imbalance would predate Earth’s current composition.
“In that work, we found that different meteorites have different isotopic signatures of potassium, which means that potassium can be used as a marker for Earth’s building blocks,” Nie said in a statement.
Armed with this clue, researchers began analyzing some of the world’s oldest known rock samples for a similar signature of potassium—and they came across a freebie. Some samples, they said, contained even less trace amounts of potassium-40. In summary, potassium-40 proto has been declining on Earth, but has gradually accumulated over billions of years. Nie and her colleagues say they ran detailed simulations showing that the fraction of potassium-40 increases over time, which reinforced their hunch.
“Scientists have tried to understand the original chemical composition of the Earth by matching the compositions of different groups of meteorites,” says Nie. “However, our study shows that the current meteorite inventory is not complete and we still need to know where our planet came from.”
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