Scientists have made an exciting discovery. They believe they have found clues pointing to the “proto-Earth,” the early version of our planet that existed before a giant impact formed the Moon. A study published in Nature Geoscience reveals chemical hints of this proto-Earth hiding in Earth’s rocks for billions of years.
“This might be the first direct proof that we have preserved the materials from the proto-Earth,” said Nicole Nie, a co-author of the study from MIT. This discovery opens a unique window into Earth’s beginnings and could help us understand what our planet and its neighbors were like long ago.
About 4.5 billion years ago, the solar system was a chaotic mix of gas and dust. This swirling cloud led to the formation of the first planets, including a young, molten Earth teeming with bubbling lava. Shortly after, a Mars-sized asteroid collided with the proto-Earth, causing massive melting and reshaping of the planet. This event created the Moon and likely erased most evidence of what Earth looked like before.
However, Nie and her team found a peculiar imbalance in potassium isotopes in ancient rocks, specifically a low amount of potassium-40. This rarity could serve as a fingerprint of the proto-Earth materials that survived the cataclysmic event. “We see a glimpse of the ancient Earth, even before the giant impact,” Nie noted, emphasizing how surprising it is to find a trace of such early evidence.
Potassium exists in three isotopes—potassium-39, potassium-40, and potassium-41. In 2023, Nie’s team studied meteorites from various parts of the solar system and found subtle differences in their potassium isotopes. This discovery indicated that these isotopes could help trace Earth’s building blocks.
To dig deeper, the researchers analyzed Earth’s oldest rocks from places like Greenland and Hawaii. They uncovered even lower amounts of potassium-40 than expected, suggesting these ancient materials come from a very different Earth. The scientists dissolved the rocks, isolated the potassium, and carefully measured the ratios of the different isotopes using advanced techniques.
Models of various geological processes, like asteroid impacts and mantle convection, couldn’t account for the potassium ratios found in the ancient rocks. This indicates that remnants of the proto-Earth remain deep within the planet, largely untouched by the giant impact.
Interestingly, while some meteorites previously studied showed potassium anomalies, they did not match this specific deficit. This hints that the materials forming the proto-Earth may still be waiting to be found. Nie points out, “Scientists have been trying to piece together Earth’s original chemical makeup. Our research shows that we still have much to learn about our planet’s origins.”
This study not only sheds light on Earth’s history but also suggests that significant discoveries lie ahead for scientists exploring the planet’s complex formation. The ongoing quest to understand Earth’s beginnings could lead to breakthroughs that reshape our knowledge of planetary formation itself.
