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Earth tipped on its side (and back again) in 'cosmic yo-yo' 84 million years ago
Earth has not always been upright. Turns out, the planet's crust tipped on its side and back again around 84 million years ago, in a phenomenon that researchers have dubbed a "cosmic yo-yo."
The actual name for the tipping is true polar wander (TPW), which occurs when the outer layers of a planet or moon move around its core, tilting the crust relative to the object's axis. Some researchers had previously predicted that TPW occurred on Earth late in the Cretaceous period, between 145 million and 66 million years ago, but that was hotly debated, according to a statement by the researchers.
However, the new study strongly suggests TPW did occur on Earth. Researchers mapped the ancient movement of Earth's crust by looking at magnetic-field data trapped inside ancient fossilized bacteria. They found that the planet tilted 12 degrees relative to its axis around 84 million years ago, before fully returning to its original position over the next 5 million years.
To test if Earth did undergo TPW during the Cretaceous, the researchers turned to magnetic minerals within limestone deposits in Italy.
"These Italian sedimentary rocks turn out to be special and very reliable because the magnetic minerals are actually fossils of bacteria that formed chains of the mineral magnetite," co-author Sarah Slotznick, a geobiologist at Dartmouth College in New Hampshire, said in the statement.
Magnetite is a highly magnetic form of iron-oxide. Some types of bacteria can create chains of tiny magnetite crystals, which naturally orient with Earth's magnetic field at the time of their creation. When these particular bacteria died and were fossilized during the period of TPW, these magnetite chains got locked in place.
Because Earth's crust moved during TPW, and not its magnetic field, these magnetic fossils (which remained in surface layers of the planet) revealed how much the crust moved relative to Earth's magnetic field over time. The team found that Earth's crust moved a total of almost 25 degrees over a period of 5 million years.
originally posted by: ColoradoTemplar
a reply to: All Seeing Eye
Hmmm that is interesting. Thank You.