The earth is not always upright. It turns out that the planet’s crust flipped sideways and back again about 84 million years ago, in a phenomenon researchers have dubbed the “cosmic yo-yo.”
The actual name for the core is true polar wander (TPW), which occurs when the planet’s outer layers or month It moves around its core, with the shell tilted relative to the object’s axis. Some researchers have previously speculated that TPW will occur Earth late from lime period, between 145 million and 66 million years ago, but that is hotly debated, according to A Statement by researcher.
However, the new study strongly suggests that TPW does occur on Earth. Researchers map ancient movements of the Earth’s crust by looking at Force field Data trapped in ancient fossils bacteria. They found that the planet tilted 12 degrees relative to its axis about 84 million years ago, before returning completely to its original position in the next five million years.
Related: 10 incredible photos of Earth taken by the Landsat satellite
“These observations represent the latest widely documented TPW and challenge the notion that [Earth’s] The spin axis has been largely stable over the last 100 million years,” the researchers wrote in their paper, which was published online June 15 in the journal. Natural Connection.
Cosmic yoyo
The Earth consists of four main layers: a solid inner core, a liquid outer core, mantle and crust. During TPW, the entire planet will appear to be upside down on its side, but actually only the outer layers are moving.
“Imagine looking at Earth from space, TPW would look like the Earth was flipping,” said co-author Joe Kirschvink, an Earth geologist at the Tokyo Institute of Technology in Japan and a professor at Caltech, in the statement. . “What is really happening is that the entire crust of the planet is rocky [the mantle and crust] It circulates around the molten outer core. “
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Individual pieces of the Earth’s outer layers are constantly moving and changing tectonic plates They collided with each other and descended under each other; But during TPW, the outer layers move together as a single unit.
As a result, the tilt of the Earth’s crust will not cause major tectonic activity or drastic changes in major ecosystems. Rather, it can be a gradual process that won’t affect me dinosaur and other living things that roam the surface.
Earth electromagnetic field It will be fixed during TPW because it is created by the liquid inner core, which will stay in place. So instead of the magnetic poles moving, the geographic poles start to wander.
petrified magnet
To test whether Earth experienced TPW during the Cretaceous, researchers turned to magnetic minerals in limestone deposits in Italy.
“This Italian sedimentary rock turned out to be very special and reliable because the ferromagnetic minerals are actually fossilized bacteria that make up the chain of magnetite minerals,” Sarah Slotznick, a geologist at Dartmouth College in New Hampshire, said in a statement. .
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Magnetite is a highly magnetic form iron-oxide. Some bacteria can create chains of tiny magnetite crystals, which align naturally with the Earth’s magnetic field at the time of its creation. When these particular bacteria die and petrify during the TPW period, these magnetite chains lock into place.
Because the Earth’s crust moves through the TPW, not its magnetic field, these magnetic fossils (which remain in the planet’s surface layers) reveal how much the crust has moved relative to the Earth’s magnetic field over time. The team found that the Earth’s crust moved about 25 degrees over 5 million years.
The researchers believe that their findings now solve the question of whether Earth contained TPW during the Cretaceous period.
“It’s refreshing to see this study with such abundant and beautiful paleomagnetic data,” said Richard Gordon, a geophysicist at Rice University in Houston who was not involved in the research, said in a statement.
Originally published in Live Science.
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