A protoplanet known as Theia slammed into the Earth about 4.5 billion years ago and a fragment resulted formed the moon. Theia must have been very large, nearly the size of Earth at the time of impact. Now, scientists say that remnants of that protoplanet can still be found, lodged deep inside Earth. Theia’s impact transformed Earth’s surface into a roiling magma ocean and later the continents formed.
Last week, Qian Yuan, a doctoral student in geodynamics at Arizona State University suggested that dense material from Theia’s mantle descended deep beneath the Earth’s surface, accumulating into what we now know as “the blobs.” “I think [the idea is] completely viable until someone tells me it’s not,” Edward Garnero, a seismologist at ASU Tempe who was not involved in the work, told Science. The theory was presented at the 52nd Lunar and Planetary Science Conference 2021. The scientists believe two mysterious dense zones 1,000 miles beneath the Earth’s surface are actually “left-over Theia mantle materials.” A 2016 NASA-funded study also postulated that the Earth could actually be two planets, itself and Theia , that fused together when they collided. The “continent-sized” areas are the largest portions of Earth’s interior, so understanding how they formed and how they persist could help push Earth science forward.