Every 202,500 Years, Earth Wanders in a New Direction

CreditJAXA/NASA

By Nicholas Bakalar

• May 21, 2018

It happens every 405,000 years. The Earth’s orbit gradually changes shape from almost circular to slightly elliptical over a period of 202,500 years, and then starts returning to form over the next 202,500 years — like a metronome swinging side to side.

Right now, we are in an almost perfectly circular orbit around the sun, and soon — within some thousands of years, that is — we will start moving toward the elliptical.

This happens because of the Earth’s gravitational interactions with other planets, especially Jupiter and Venus — Jupiter because it is very large, and Venus because it is very near.

In new research published in the Proceedings of the National Academy of Sciences, scientists tracked the orbital cycle by analyzing a 1,700-foot-long rock core drilled in the Petrified Forest National Park in Arizona.

The 405,000-year cycle, they found, has held uniform into the very distant past — back to at least 215 million years ago.

So the scientists linked the climate cycles of the Northeast sediments with the accurate uranium-lead dates from the Arizona core. The timing matched: the variations in both showed that the 405,000-year cycle has been going on precisely as scientists had calculated.

What does knowing this mean? The lead author of the study, Dennis V. Kent, a professor of earth and planetary sciences at Rutgers University, said that it will give scientists a much more accurate method of dating prehistorical events — the dates of fossils, for example.

“The dream is have a framework independent of the fossils that you can plug the fossils into and see more interesting things — the coexistence of disparate forms, or of similar forms widely separated in location. Now we can place things more accurately in time rather than depending on the fossils to tell us what the time is.”

“And this is an interesting time,” he added. “Dinosaurs and mammals first appeared 252 to 201 million years ago.”

Correction:

A headline in an earlier version of this article misstated the number of years it takes Earth to change directions. It is 202,500, not 202,500 million.

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