A fragment of the primitive Earth, dating back 4.5 billion years, survived the Giant Impact

It is said that a face preserves the traces of life, just as the rocks of the Earth preserve the testimony of the past. Except that for the oldest testimonies, time gradually erases their traces.

The discovery just announced by a team of researchers from MIT and elsewhere is quite astonishing: they believe they have isolated evidence and traces of rocks that date from before the famous impact which caused the formation of the Moon, 4.5 billion years ago. A true archaic treasure.

The anomaly in the rock that reveals the unthinkable

4.5 billion years ago, the Earth was struck by a wandering planet the size of Mars and from this giant impact the Moon was born. There is a real scientific consensus on this event, although finding direct evidence is very complicated. Indeed, the rocks alter over time and the magma furnace caused by the impact modified the chemical structure of the terrestrial rocks.

However, an international team of researchers has just published the fruit of their work in Nature, and it seems to have solid proof that the Earth contains a witness to this very ancient, and even primitive, era.

They obviously did not dig thousands of kilometers under the crust and into the Earth’s mantle. This is not within the reach of our machines. They used the precision of a mass spectrometer which makes it possible to know very precisely the nature and quantity of such and such atoms in a grain of rock dust. And the witness who was willing to speak is called: potassium 40.

It was by analyzing samples of very ancient rocks (from Greenland and Canada) as well as deep lavas from Hawaii (which rise from the Earth’s mantle), that the team identified a tiny but crucial anomaly in the quantity of this type of potassium. Imbalance which cannot have been caused by more recent impacts according to her. This rock lacks potassium 40 compared to all other terrestrial rocks as well as compared to known meteorites, making it a chemical marker necessarily dating from the first hundred million years of the planet.

“This may be the first direct evidence that we have preserved materials from Proto-Earth,” explains Nicole Nie, assistant professor at MIT. “We see a piece of the very old Earth, even before the giant impact. This is amazing because we expected this very early signature to slowly be erased.”

Computer simulations that confirm the hypothesis

By simulating the chemical evolution of the Earth after theGiant Impact and other meteorite impacts, the scientists confirmed that their models produced the modern composition (without the potassium-40 deficit). The fact that the actual samples retain this deficit is therefore strong evidence that these materials were not entirely mixed with the rest of the planet after the collision.

The consequences of such scientific work could involve a rewriting of the origins of the Earth and give geologists and planetary scientists a unique reference for determining the primordial ingredients that formed our planet, or even the Solar System.

This discovery also tends to show that the evolution of the continents is even slower than previously imagined.

And last rather fascinating point, as the analysis of this rock does not correspond exactly to the meteorites collected and studied, this seems to indicate that certain “bricks” of construction of the Earth remain unknown…