Amazing stuff!
"Scientists ... have discovered extremely rare remnants of “proto Earth,” which formed about 4.5 billion years ago, before a colossal collision irreversibly altered the primitive planet’s composition and produced the Earth as we know today. ...
In this earliest phase, Earth was likely rocky and bubbling with lava. Then, less than 100 million years later, a Mars-sized meteorite slammed into the infant planet in a singular “giant impact” event that completely scrambled and melted the planet’s interior, effectively resetting its chemistry. Whatever original material the proto Earth was made from was thought to have been altogether transformed. ...
The researchers have identified a chemical signature in ancient rocks that is unique from most other materials found in the Earth today. The signature is in the form of a subtle imbalance in potassium isotopes discovered in samples of very old and very deep rocks. The team determined that the potassium imbalance could not have been produced by any previous large impacts or geological processes occurring in the Earth presently.
The most likely explanation for the samples’ chemical composition is that they must be leftover material from the proto Earth that somehow remained unchanged, even as most of the early planet was impacted and transformed. ..."
From the abstract:
"Earth’s bulk composition has elemental and isotopic characteristics that cannot be fully reconciled with a mixture of known primitive meteorite compositions. One potential explanation for this is that the proto-Earth accreted materials with isotopic signatures distinct from those accreted after the Moon-forming giant impact.
Here we report high-precision mass-independent potassium isotopic measurements from thermal ionization mass spectrometry of terrestrial rocks from various ancient and modern sources in the crust and mantle that we argue are consistent with this explanation.
Specifically, we found that some mafic Archaean rocks derived from the Hadean–Eoarchaean mantle (including samples from Isua, Nuvvuagittuq and the Kaapvaal Craton) and certain modern ocean island basalts (from La Réunion Island and Kama’ehuakanaloa volcano, Hawaii) exhibit an average 40K deficit of 65 parts per million compared to all other terrestrial samples analysed. The deficit distinguishes these samples from the bulk silicate Earth and any known meteorite group and cannot result from magmatic processes. Therefore, we propose this 40K deficit represents primitive proto-Earth mantle domains that largely escaped mantle mixing after the giant impact and exist in the present-day deep mantle, contributing to some modern hotspot volcanism."
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