The surface of our planet is simply too active for rocks to stay around for long, but geologists might have just discovered that some of the original material from the mantle has survived over the entirety of Earth’s history.
An international team of researchers has discovered rocks in two separate locations with the highest concentration of tungsten isotopes ever measured in Earth’s basalts. This tungsten abundance can only be explained by the processes that were going on in the early Solar System, so the researchers are confident that they discovered material that formed when our planet was less than 50 million years old.
The 182-tungsten isotope has a similar low abundance across almost all rocks of the planet, but some of the oldest rocks have an excess of 15 parts per million or less. The silicate mineral in the study, found in Baffin Bay in the North Atlantic and Ontong Java Plateau in the western Pacific Ocean, have an excess between 10 to 48 parts per million. The results are reported in this week's Science.
The material was part of Earth’s mantle, the thick layer of hot silicate between the metallic core of our planet and the crust. The mantle is mostly solid, but over geological times, it behaves like a viscous liquid with convection mechanisms. This discovery shows that a portion of the mantle has remained unchanged since the planet formed 4.6 billion years ago.
“What we’ve found are surviving parts of Earth’s primitive mantle that have been preserved for four and a half billion years, and I think that’s kind of exciting!” Professor Richard Walker, co-author of the study, said in a statement.
Earth is believed to have formed by the progressive accretion of material through the collision of bodies during the first few million years of the Solar System. The most important of these collisions is the impact between the proto-Earth and an object the size of Mars, which led to the formation of the Moon.
This discovery might give us a better understanding of the composition of the early Solar System and the material that eventually became our planet.
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