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Earth's poles shifted surprisingly fast during the age of dinosaurs, ancient sea levels reveal
The events, the most recent of which occurred 10—20 million years ago, saw the geographical poles shift by up to 0.6 degrees per million years — faster than plate tectonics.
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The location of Earth's geographic poles has changed several times over the past 320 million years in a process known as true polar wander, according to measurements of ancient flooding brought about by sea level changes resulting from our planet's crust shifting relative to Earth's spin axis.
Such a shift can affect climate, both on local scales and globally, as regions that were by the poles find themselves moving down to lower latitudes and vice versa. This can then affect atmospheric circulation patterns, which affect climate across the world.
The changes would have affected the environments in which life developed and evolved, from the age of the dinosaurs through to some of our oldest primate ancestors.
True polar wander is not the same as a change in the rotational axis of the Earth. Currently, Earth spins at an angle of 23.4 degrees relative to the plane of its orbit around the sun, and this rotational axis can vary periodically over tens of thousands of years as a result of the Milankovitch cycles caused by the gravitational pull of the sun and planets.
True polar wander is different. Here, the angle of Earth's spin axis does not change relative to its orbital plane. Instead, Earth's crust and mantle shift relative to that rotational axis. This is because Earth is not perfectly spherical. Instead, it is oblate, with Earth's rotation causing the equator to bulge out and the poles to slightly flatten. Because Earth is not spherical, it has multiple axes of inertia, the largest one being aligned with the rotational axis.
These axes need to be balanced to prevent Earth's rotation from becoming chaotic. However, plate tectonics and indeed the Milankovitch cycles can upset that balance of mass, for example by causing more continental crust to congregate in one hemisphere than another.
To rebalance things, Earth's crust and mantle must become decoupled from our planet's core, which stays aligned with the rotational axis. In physical terms, if there is more continental crust in one hemisphere, the crust and mantle might rotate in that direction relative to the rotational axis and the Earth's core in order to balance itself. This sees the geographical locations of the poles change, hence the name 'true polar wander'.
Currently, true polar wander takes place at a rate of 10 centimeters (4 inches) per year, but figuring out when and how fast true polar wander has occurred in the past is not without its difficulties, not least since plate tectonics can mask and even mimic the signal of true polar wander.