‘True polar wander’ may have caused ice age

[Elderberry]

Rice University 11/19/2018 by Jade Boyd

Earth’s latest ice age may have been caused by changes deep inside the planet. Based on evidence from the Pacific Ocean, including the position of the Hawaiian Islands, Rice University geophysicists have determined Earth shifted relative to its spin axis within the past 12 million years, which caused Greenland to move far enough toward the north pole to kick off the ice age that began about 3.2 million years ago.

Their study in the journal Geophysical Research Letters is based on an analysis of fossil signatures from deep ocean sediments, the magnetic signature of oceanic crust and the position of the mantle “hot spot” that created the Hawaiian Islands. Co-authors Richard Gordon and Daniel Woodworth said the evidence suggests Earth spun steadily for millions of years before shifting relative to its spin axis, an effect geophysicists refer to as “true polar wander.”

“The Hawaiian hot spot was fixed, relative to the spin axis, from about 48 million years ago to about 12 million years ago, but it was fixed at a latitude farther north than we find it today,” said Woodworth, a graduate student in Rice’s Department of Earth, Environmental and Planetary Sciences. “By comparing the Hawaiian hot spot to the rest of the Earth, we can see that that shift in location was reflected in the rest of the Earth and is superimposed on the motion of tectonic plates. That tells us that the entire Earth moved, relative to the spin axis, which we interpret to be true polar wander.”

By volume, Earth is mostly mantle, a thick layer of solid rock that flows under intense pressure and heat. The mantle is covered by an interlocking puzzle of rocky tectonic plates that ride atop it, bumping and slipping against one another at seismically active boundaries. Hot spots, like the one beneath Hawaii, are plumes of hot solid rock that rise from deep within the mantle.

Gordon, the W.M. Keck Professor of Earth, Environmental and Planetary Science, said the new findings build on two 2017 studies: one from his lab that showed how to use hot spots as a global frame of reference for tracking the movement of tectonic plates and another from Harvard University that first tied true polar wander to the onset of the ice age.

More: http://news.rice.edu/2018/11/19/true-polar-wander-may-have-caused-ice-age-2/