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!
You don’t need to do the math … 4.5 billion years ago dates back to the birth of Planet Earth and that’s why University of Maryland Professor of Geology Richard Walker is as excited as a geologist can be. He led a team of researchers that discovered a pair of what are being called “birthmarks” made of silicate material formed when Earth was less than 50 million years old.
Is this really big news? According to Walker’s report in the current edition of the journal Science, it’s the first time that original material from the birth of Earth has been discovered. Until now, the accepted scientific belief was that any material from the planet’s original mantle (the layer between the crust and the outer core) was destroyed or changed beyond recognition by collisions with space bodies during the formation of the solar system, especially the big one (the so-called Theia impact) with a Mars-sized body named Theia that created the Moon.
This rock-solid belief began to crumble Richard Walker when Walker’s team looked at lava rocks from Baffin Island off the coast of northern Canada and from the Ontong-Java Plateau in the Pacific Ocean, north of the Solomon Islands. They found that these rocks contained a significant amount of an isotope of tungsten-182. So? It turns out that this isotope was only formed from decaying hafnium-182 during the first 50 million years of the solar system and never again. That means it’s an original “birthmark” of Earth.
How did these birthmarks survive? The researchers theorize that the mantle under Baffin and Ontong-Java did not experience the same tungsten-removing iron separation that the rest of the mantle experienced during the collisions that destroyed or homogenized the rest of early Earth. It was brought to the surface during volcanic eruptions 60-to-120 million years ago and only now detected by devices that can identify the tungsten-182 isotope.
Now that they know what to look for, Walker believes that more Earth birthmarks will be found and that will lead to a better understanding of the formation of both the planet and the solar system.
Walker is right. That IS kind of exciting.