Scientific analysis of geological data from the Marche region suggests 84 million years ago the Earth’s axis tilted to one side, and then back. This is known as true polar wander.
The Earth’s spin axis shifts slowly over time. It can take millions of years for just on degree of change. During that process, the geographical location of the North and South magnetic poles changes accordingly.
There is a theory among geophysicists that faster and more extreme oscillations occurred during the Cretaceous period.
Analysing rocks from Le Marche
An international team, led by Ross Mitchell from the Chinese Academy of Sciences, has spent seven years recording and analysing data from rock samples found in central Italy. Among the team is palaeontologist, Rodolfo Coccioni, from Università di Urbino, reports Nature.com.
“Stratigraphic sections from Furlo and Apiro in the Marche region are largely composed of ‘scaglia rossa’, a sedimentary rock full of microfossils that simplifies the dating process” Coccioni explains.
What is incredible is the hematite and lodestone in those rocks have microscopic natural magnets embedded in them. These natural magnets retain signs of the position of magnetic poles in the past, even after millions of years.
The scientists collected data from two parallel stratigraphic samples dating to the same era, collected from the same site and analysed with the same methods, to ensure that the corresponding results were no accident.
The data shows that in the Late Cretaceous period, about 84 million years ago, the Earth’s spin axis started to change. As a result, Italy moved to lower latitudes. The estimation is of a variation of 12 degrees. Then the process reversed. 78 million years ago the axis returned to its original position.
“The axis probably took a round trip’” says Coccioni. “Our data fit with what we call a true polar wander, consisting in this notable shift in spin axis”.
Old theory, newer techniques
This is not a new hypothesis. Indeed, an earlier analysis on similar rocks from a site in Umbria in the 1970s appeared to disprove it.
However, now Coccioni and the team have more precise techniques unavailable in the 1970s. The scientists theorise the tectonic plates drifted causing an unbalanced weight distribution on the Earth surface. This then forced the planet to tilt. “But more data from other parts of the world are needed to confirm that a true polar wander occurred” says Coccioni.
