Space.com reports:

Scientists have identified what may be the first direct evidence of material left over from the “proto-Earth,” a primordial version of our planet that existed before a colossal moon-forming impact reshaped it forever.

The study, published Tuesday (Oct. 14) in the journal Nature Geoscience, suggests that tiny chemical clues of this proto-Earth have survived deep within Earth’s rocks, essentially unaltered, for billions of years. The findings provide a rare window into the planet’s original building blocks and could offer scientists clues about what Earth and its neighboring worlds were like in their earliest eras.

“This is maybe the first direct evidence that we’ve preserved the proto-Earth materials,” Nicole Nie, an assistant professor of Earth and planetary sciences at MIT who co-led the new paper, said in a statement.

Roughly 4.5 billion years ago, the young solar system was a swirling cloud of gas and dust that formed the first asteroids and planets, including the young Earth, then a hot, molten sphere likely bubbling with oceans of lava.

Less than 100 million years later, a Mars-sized asteroid collided with the proto-Earth in an event so violent it melted and remixed nearly the entire planet, creating the moon in the process. It was the last event to cause large-scale melting of Earth’s mantle, the new study notes, and scientists have long suspected that this “giant impact” wiped away nearly all chemical traces of what came before.

But Nie and her colleagues uncovered a subtle imbalance in potassium isotopes in ancient rock, specifically a deficit of potassium-40. This anomaly, the researchers argue, is a potential fingerprint of material that survived from the proto-Earth itself. [Continue reading…]