Arabia Weather – Researchers say that the strangely dense rocks in the inner layer are the result of a collision that occurred 4.5 billion years ago.
Many scientists believe that about 4.5 billion years ago, a Mars-sized object collided with Earth, spewing out debris that combined to form the Moon. Some remnants of this object, called Theia, still exist today in the form of large amounts of dense material located above the Earth’s core
In recent years, geophysicists have discovered continent-sized areas of rock at the bottom of the Earth’s interlayer where seismic waves travel abnormally slowly, indicating that the rocks there are denser than the rest of the layer’s rocks. One of these spots, known as large low-density provinces, lies beneath the continent of Africa, while the other lies half a world away beneath the Pacific Ocean, according to planetary geodynamicist Qian Yuan of the University of California, Technology Institute.
Some researchers have suggested that these blocks are the remains of tectonic plates that were pushed under the tectonic plates and then sank to the boundary between the Earth’s outer core and the upper layer. But Yuan and his colleagues offer a different origin story.
The Moon is only about 2% of Earth’s mass, leaving a significant amount of Theia unexplained. So, using a supercomputer simulation, the researchers tracked the effects of a collision between Earth and another object with a mass roughly 10 percent of Earth’s mass.
In the simulation, each object before impact had a dense iron core surrounded by a light rock crust. Each object was digitally divided into particles about 10 kilometers in diameter, so that fragments could be tracked after impact, explained one of the study’s authors, Vincent Eck, a computational physicist at Durham University in England. He points out that the team’s simulations tracked about 100 million particles.
Simulations suggest that a significant portion of Theia’s core — equivalent to about 3% of Earth’s current mass — was left behind on the planet. Shortly after the impact, this dense, molten material would have sank to join the Earth’s core. Meanwhile, the research suggests that a significant portion of Theia’s crust — amounting to about 5% of Earth’s mass — was embedded in the upper 1,400 kilometers or so of Earth’s surface.
Lunar rocks indicate that Theia’s crust contained higher levels of iron oxide minerals. This means it was likely a few percent denser than Earth’s interlayer, Qian says. The researchers suggest that during the few decades following the impact, this denser-than-average material slowly fell to accumulate and form large low-velocity provinces.
Although many researchers have suggested that these low-velocity provinces are remnants of tectonic plates, others have suggested that they are high-density remnants of Earth’s original magma ocean that submerged to the lowest levels of Earth’s interlayer. “Attributing it to material left behind by the collision between Theia and the emerging Earth is a new idea, apparently,” says Paul Tackley, a geodynamist at TH Zurich University, who was not part of the new study.
Whether or not a collision with Theia resulted in the low-density provinces, it is at least possible that they have been extending for approximately 4.5 billion years since the moon formed, Takeli says. If the material in these regions is dense enough to resist mixing with the overlying layer as it flows slowly through it, it can persist over geological time.
“Giant impact hypothesis”
The collision between Earth and a protoplanet, known as… “Giant Impact Hypothesis” The leading theory on how the Moon formed. Previously, researchers suggested that such a collision would help explain subtle chemical differences between Moon rocks and Earth rocks. Scientists have recently suggested that the collision between Earth and Theia, in addition to creating our Moon, also initiated the process of plate tectonics.
Source: sciencenews
