Linked to the planet’s earliest history, this discovery may open a new window into how Earth first came together.
Researchers have uncovered what could be the oldest surviving fragment of our planet—material that predates the Moon itself. A new study led by scientists at the Massachusetts Institute of Technology (MIT), in collaboration with teams from China, Switzerland, and the United States, identifies a chemical signature in ancient rocks that may represent the first tangible evidence of proto-Earth—the version of our planet that existed before a catastrophic impact reshaped it 4.5 billion years ago.
Published in Nature Geoscience, the findings suggest that traces of Earth’s original composition still linger deep within its interior. If confirmed, this discovery would rewrite what scientists know about how the planet formed and evolved.
A Collision That Rebuilt the Planet
According to the dominant theory of planetary formation, Earth emerged from a swirling disk of gas, dust, and rock orbiting the young Sun. Over millions of years, these fragments collided and merged, creating a molten, unstable world.
Roughly 100 million years later, that early Earth was struck by a Mars-sized object—an event known as the giant impact. The collision vaporized vast amounts of material, generating the debris that would eventually form the Moon. It also melted and mixed much of Earth’s mantle, effectively resetting the planet’s chemistry and leading researchers to believe that its original building blocks were lost forever.
MIT scientists have found amazing clues about Earth’s early history:
– Rocks from 4.5 billion years ago were found in Greenland, Canada, and Hawaiian lava.
– These rocks have very little potassium-40, which challenges the usual Moon-formation theory.
– Computer simulations say… pic.twitter.com/L9t6gnBHTL— Tornado guy (@fanofaliens) October 15, 2025
Isotopic Evidence Buried in Ancient Rocks
To test that assumption, the MIT-led team analyzed ancient rock samples from Greenland, Canada, and volcanic sites in Hawaii—regions that hold some of Earth’s oldest and least-altered geological material. Using ultra-precise mass spectrometry, the researchers measured the ratios of three potassium isotopes: K-39, K-40, and K-41.
They detected a small but consistent deficit in potassium-40, a radioactive isotope that naturally decays into argon over time. This anomaly had never been seen in modern rocks. Its presence implies that these materials were somehow shielded from the violent mixing caused by the Moon-forming impact.
“This could be the first direct evidence that proto-Earth material still exists,” said Nicole Nie, planetary scientist at MIT and the study’s lead author. “Finding a chemical fingerprint that survived from before the giant impact is extraordinary given how dynamic our planet has been.”
Beyond Earth: A Missing Link in Planetary Chemistry
Nie and her colleagues previously studied meteorites from across the solar system, mapping their potassium isotope signatures to reconstruct where and how they formed. None of those extraterrestrial samples matched the unusual signature now found in Earth’s mantle rocks. That gap implies that the primordial material that built Earth may not be represented in any known meteorite collection.
To verify their results, the team simulated how Earth’s potassium isotope ratios would evolve under billions of years of mantle convection, radioactive decay, and repeated impacts. Every model predicted higher levels of potassium-40 than the team observed in the ancient samples—strong evidence that part of Earth’s deep interior still preserves its pre-impact chemistry.
What Earth Was Before It Was Earth
The collaboration—spanning MIT, the Chengdu University of Technology, the Carnegie Institution for Science, ETH Zurich, and the Scripps Institution of Oceanography—adds a vital new piece to the puzzle of Earth’s origins. By identifying a distinct isotopic “fingerprint” from before the Moon existed, scientists have found a tool for tracing the earliest materials that shaped the planet.
Traditionally, researchers have inferred Earth’s early composition by comparing it with meteorites. This study challenges that approach. “The current meteorite inventory is not complete,” Nie noted. “We’re realizing that parts of Earth’s foundation may have formed from materials we’ve never seen elsewhere in the solar system.”
The discovery suggests that Earth’s story began earlier and survived deeper than anyone expected—and that the last traces of our planet’s birth are still hidden beneath our feet.
