Jakarta –
True polar wander (TPW) can sometimes tilt the entire planet and Moon, relative to its axis. It is not known exactly how often this happens on Earth. But there is evidence that Earth been tilted millions of years ago.
TPW is the rotation of a solid body of a planet or Moon with respect to its axis of rotation. This causes the geographic locations of the north and south poles to change, or “wander”.
A recent study provides evidence of a single event Earth tilted as it did about 84 million years ago, a time when dinosaurs were still living on Earth.
The researchers analyzed limestone samples from Italy, which date back to the Late Cretaceous period (100.5 to 65.5 million years ago). They are looking for evidence of a shift in the magnetic record that would lead to the occurrence of TPW.
Fossil bacteria trapped in rock, forming chains of the mineral magnetite. It offers some of the most compelling evidence of late Cretaceous polar wandering, and may help settle decades of scientific debate.
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A picture of when the Earth experiences a true polar wander which causes it to tilt. Photo: Wikimedia Commons– |
“These observations represent the latest documented large-scale TPW and challenge the idea that the spin axis has been largely stable over the last 100 million years,” the researchers said in their paper.
The Earth consists of a solid metal inner core and a liquid metal outer core, with the solid mantle and crust (surface) moving slowly over the molten metal. The Earth’s magnetic field, generated by the outer core, is recorded in rocks as studied in this study.
When TPW occurs, the Earth’s outer layer is tilted. Nothing has really changed in terms of the Earth’s magnetic field. However, shifting rocks will record different paleomagnetic data as they move.
The data revealed the distances to the geographic North and South poles, allowing researchers to plot where these poles actually are. A completely vertical plane means the rock is at the poles, while a completely horizontal plane indicates that the rock is at the equator.
“Imagine looking at Earth from space. A true polar odyssey would look like a tilted Earth, and what’s really happening is that the entire rocky shell of the planet, aka Earth’s solid mantle and crust, revolves around a molten outer core,” said geologist Joe Kirschvink of the Tokyo Institute of Technology in Japan.
According to research, Earth tilted about 12 degrees at 84 million years ago. But this tilt is corrected relatively quickly, i.e. it returns to its origin in about 5 million years. That is, these rocks traveled towards the equator before tipping over.
The research team said previous studies suggested that TPW did not occur during the Late Cretaceous. At that time, there was not enough data from the geological record to prove it.
“That’s one of the reasons why it’s so exciting to see this study with its rich and beautiful paleomagnetic data,” said geophysicist Richard Gordon of Rice University in Houston.
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