Published On 19/10/2025
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Last update: 10:13 (Mecca time)
Deep within our planet, hundreds of kilometers beneath the crust on which we walk, it seems that history has not been completely erased. There, between the molten rocks and the enormous pressure, hide traces of a “lost world”: remnants of the ancient Earth from which our modern Earth was born more than 4 billion years ago.
And according to study Published by researchers from the Massachusetts Institute of Technology in the journal Nature Geoscience, a “strange chemical fingerprint” was found in rock samples from deep within the crust and upper regions of the mantle.
This fingerprint suggests that parts of the “first Earth” – that planetary mass that later collided with a giant body to form our current planet and the Moon – are still alive in the bowels of the Earth.
Potassium brothers
The story began when geochemists decided to trace potassium isotopes in very ancient rocks collected from areas such as Greenland, Canada, and the Hawaiian Islands.
These isotopes are atoms of the same element, meaning they have the same number of protons, but they differ in the number of neutrons inside their nucleus.
In simpler terms, imagine that all of the element’s atoms are “siblings” of the same family, with the same name (such as potassium) but slightly different weights because some of them carry more or fewer neutrons. For example: potassium-39 and potassium-40 are isotopes of the same element (potassium).
Potassium is a common element in rocks, but the ratios of its isotopes can reveal deep secrets. Potassium-40 decomposes slowly over time, and its distribution in rocks reflects the processes that occurred during the formation of the Earth and its differentiation into a core, mantle, and crust.
Chemical fingerprint
But the surprise came when researchers noticed a slight decrease in potassium-40 levels compared to what is expected in normal Earth rocks, according to this study.
She says this lack of radioactive isotopes can only be explained if some parts of the Earth’s mantle never mixed with the rest of the planet after the giant collision between the first Earth and a Mars-sized body known as Theia, an event that is believed to have created the Moon.
At that time, the Earth turned into an ocean of magma in which minerals boiled and the layers were mixed together like a huge cosmic dough. However, it appears that some deep corners of the mantle remained “protected” and were not reached by complete melting or cosmic mixing.
These insulating pockets remained as “temporal storage rooms,” carrying within them the imprint of the ancient land as it was before its features changed.
Unexpected date
The importance of the discovery is that it gives scientists a rare opportunity to look inside the early stages of Earth’s formation. Since planets began gathering from cosmic dust in the disk surrounding the sun, chemical reactions and violent thermal activity have been constantly erasing traces of the past.
However, the survival of chemical traces from the first Earth means that we have physical evidence of our origin before we became “the Earth as we know it.” It is like finding fragments of a cosmic manuscript in the interior of rocks, in which there is text written in the language of atoms that tells us about beginnings that we did not see.
To convince the scientific community, the MIT team used physical and geochemical models showing how some regions in the deep mantle could have remained isolated for so many billions of years.
As the Earth’s plates move, the depths of the mantle – especially at its boundary with the iron core – may remain relatively stagnant, out of reach of the convection currents that mix the layers.
These areas are known among geologists as “low-velocity zones”, which are huge spots under Africa and the Pacific Ocean, and may represent stores of ancient, unmixed material.
This may be the place that still retains the memory of the first Earth, as if it were rocky ghosts from a planet that was born before the Earth itself was complete.
Planetary view
This is not limited to rewriting Earth’s history, but also extends to our understanding of how other rocky planets, such as Mars and Venus, and even distant exoplanets formed.
If the Earth has preserved pieces of its first matter despite massive collisions and thermal changes, this means that the process of planetary differentiation (the transformation from a rocky ball to a planet with a core, a mantle, and a crust) is not completely homogeneous as scientists previously thought, and perhaps other planets carry within them similar “archaeological” layers that have not yet merged into a unified entity.
This opens a new door to comparative planetary science. If we can identify similar fingerprints in volcanic rocks from Mars, the Moon, or even asteroids, we may be a step closer to reconstructing the chemical history of the solar system.
Despite the enthusiasm, questions remain open: How large are these ancient pockets in the ground? Are its thermal or wave properties different from the rest of the mantle? Could it have affected the shape of the continents, the movement of plates, or even volcanic activity?
Answers require new tools, from deep earthquakes to laboratory experiments that simulate mantle pressure.
But what is certain is that this discovery redraws the map of our planet’s identity. The Earth is not just a homogeneous body, but rather a time mosaic containing layers of history, some of which are still pulsing from an era that we did not know still existed.