A recent study says that about 20 years ago, a satellite detected strange gravitational signals off the coast of Africa, suggesting that something unusual was happening deep within the Earth, distorting the gravitational field.
A large-scale gravity anomaly lasted for about two years in the eastern Atlantic Ocean. It peaked in January 2007, the same month Steve Jobs introduced the first iPhone (of course, there was no connection between the two events).
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Researchers suspect that this strange anomaly and sudden movement may be caused by a previously unknown geological process. Their findings, published Aug. 28 in the journal Geophysical Research Letters, showed that changes in mineralogy may have caused a rapid redistribution of mass deep in the mantle near the core, altering Earth’s magnetic field.
Study co-author Mioara Mandea, a geophysicist at France’s National Center for Space Research (CNES) and principal investigator of the European Research Council’s Gravimetry, Magnetism, Rotation and Core Flows project, told Live Science that she initially doubted the validity of the signal.
“As is often the case in scientific research, my first reaction was to wonder if the signal was real, how could it be verified, and how should it be interpreted?” Mandea said in an email. “While the results and their publication were certainly satisfactory, the prevailing thought was to consider next steps and possible implications.”
The GRACE satellites were two identical spacecraft operated as part of a joint mission between NASA and the German Aerospace Center (DLR). Scientists used these satellites, which were active from 2002 until they ran out of fuel in 2017, to measure variations in Earth’s gravity. According to NASA, the satellites moved in parallel (back and forth) around the Earth, and researchers measured the distance between the two objects to look for changes that occurred as a result of fluctuations in Earth’s gravity.
Such variations in gravity are often caused by variations in mass concentration. The greater the mass, the greater the force of gravity. For example, water currents displace mass within the oceans, which can cause local fluctuations in Earth’s gravitational field. In the new study, researchers scoured GRACE data and found an unusual gravity signal that may have originated deep within the Earth, rather than water moving on or near the surface.
The signal is a north-south gravity anomaly that spread for about 4,350 miles (7,000 kilometers) from 2006 to 2008, nearly the length of the entire continent of Africa, according to the study.
Although researchers are still studying Earth’s deep mantle and the interface between rocky layers and Earth’s liquid outer core, the lower part of the mantle is primarily composed of magnesium silicate (MgSiO3). The study authors suggested that the redistribution of mass attributed to this signal may be the result of a perovskite-to-post-perovskite phase transformation in this lower mantle region, which changes the structure of the magnesium silicate under pressure and moves mass deeper into the Earth.
Mandea pointed out that the main message of the study is that the Earth is complex and understanding its internal processes requires different datasets and methodologies.
“Earth is a complex system that needs to be studied using diverse datasets and complementary analytical methods,” Mandea said. “This synergy provides an opportunity to uncover and better understand hidden processes deep within the Earth.”
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