By Will Dunham
WASHINGTON (Reuters) – Seismologists have long known about the existence of two enigmatic continent-sized blobs deep within the Earth’s mantle: one beneath Africa and the other beneath the South Pacific region.
These dense blobs, which are denser than the surrounding material, may hold the key to understanding a cataclysmic event that occurred early in our planet’s history. Scientists hypothesize that these blobs are remnants of a collision between Earth and a Mars-sized object called Theia that is believed to have given birth to the moon. Researchers presented this fascinating theory on Wednesday.
According to recent research, this epic collision took place a staggering 4.46 billion years ago. The impact generated molten rock that was flung out into space, eventually coalescing to form the moon. However, fragments of Theia could have remained within our planet, sinking to a location just above the intensely hot core composed of iron and nickel.
The scientists conducted computer simulations to analyze the impact event, the geophysical properties of Theia, and the evolution of Earth’s mantle, which is the widest layer in the planet’s interior structure, reaching a depth of approximately 1,800 miles (2,900 km).
Based on these simulations, the researchers propose that most of Theia merged with Earth, forming the two blobs, while leftover debris transformed into the moon we see today.
“These blobs lie 2,900 kilometers below our feet and account for approximately 2% of Earth’s mass. Seismic waves travel at a slower pace within these regions compared to the surrounding mantle, enabling their detection. Each blob is twice as massive as the moon itself. Hence, they can be considered colossal,” said Qian Yuan, lead author of the study and a geophysicist from Caltech. Their findings were published in the journal Nature.
If the conclusions drawn from this study are correct, these blobs would provide the first tangible evidence of the hypothetical moon-forming collision.
“Until now, there has been limited consensus on whether we could find evidence for this event, not just in the moon but also in observable characteristics of our present-day Earth,” explained Paul Asimow, a study co-author and geology and geochemistry professor at Caltech.
Additionally, according to Asimow, these two blobs represent the most significant deviations in Earth’s structure from a simple layered planet.
“It is truly remarkable that, by delving deep into Earth’s mantle, we may uncover remnants of another planet – Theia,” added Hongping Deng, a planetary scientist from the Chinese Academy of Sciences’ Shanghai Astronomical Observatory and another co-author of the study.
The higher density observed in the blobs is believed to be a result of their iron-rich composition, similar to moon rocks. This observation supports the notion that they are formed from the same source material as Theia.
“Following the impact, these materials would have sunk down to the core-mantle boundary due to their higher density compared to the surrounding mantle. It is this excess density that has allowed them to survive throughout Earth’s long history,” explained Yuan.
The moon, which orbits Earth at an average distance of about 239,000 miles (385,000 km), has a diameter of approximately 2,160 miles (3,475 km), slightly over one-fourth the size of Earth.
Asimow suggests that, if their conclusions are accurate, some volcanic rocks that reach the Earth’s surface might provide samples from a vanished planet.
“If our model holds true, then the blobs should contain isotopes and trace elements similar to those found in mantle rocks on the moon. Future lunar missions can test this hypothesis,” said Yuan.
Understanding this colossal collision could yield invaluable insights into the evolution of Earth and other rocky planets within our solar system and beyond.
“We suspect that significant impacts are common during the final stages of the accretion process for all terrestrial (rocky) planets and exoplanets,” added Asimow. “As we strive to develop a catalog of potential planet outcomes – determining the likelihood of planets resembling Earth rather than Mars, Mercury, Venus, or none of the above – it is important that we comprehend the consequences of such impacts.”
(Reporting by Will Dunham, Editing by Rosalba O’Brien)
