The Earth rolled over on its side 84 million years ago

The Earth rolled over on its side 84 million years ago

The real name for the reversal is true polar wander (TPW), which occurs when the outer layers of a planet or moon move around its core, tilting the crust with respect to the axis of the object. Some researchers had previously predicted that TPW occurred on Earth at the end of the Cretaceous period, between 145 million and 66 million years ago, but this has been hotly debated, according to a statement by the researchers.

However, the new study strongly suggests that TPW occurred on Earth. Researchers have mapped the ancient movement of the earth's crust by observing magnetic field data trapped inside ancient fossilized bacteria. They found that the planet tilted 12 degrees from its axis some 84 million years ago, before completely returning to its original position over the next 5 million years.

Individual pieces of the outermost layers of the Earth are constantly moving and changing as the tectonic plates collide and subduct one under the other; but during the TPW, the outer layers move together as a single unit. Consequently, the inclination of the earth's crust would not have led to any major tectonic activity or drastic changes in the main ecosystems. Instead, it would have been a gradual process that would not have impacted the dinosaurs and other living things walking the surface.

Earth's electromagnetic field would have been static during the TPW because it is created by the liquid inner core, which it would remain in place. So rather than the magnetic poles that move, it is the geographic poles that begin to wander. To check whether the Earth underwent TPW during the Cretaceous, the researchers turned to magnetic minerals within limestone deposits in Italy.

Magnetite is a highly magnetic form of iron oxide. Some types of bacteria can create chains of tiny crystals of magnetite, which naturally orient themselves with the Earth's magnetic field when they are created. When these particular bacteria died and were fossilized during the TPW period, these magnetite chains were locked in place.

As the earth's crust moved during the TPW, and not its magnetic field, these magnetic fossils (which remained in the surface layers of the planet) revealed how much the crust has moved relative to the Earth's magnetic field over time. The team found that the earth's crust has shifted a total of nearly 25 degrees over a period of 5 million years.

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