Jupiter and Venus Are Shifting Earth's Orbit Every 405,000 Years

Jupiter and Venus are pushing Earth's orbit off-kilter. Every 405,000 years, the Earth swings from a nearly circular path to a much more elliptical route around the sun because of the gravitational influence of these nearby behemoths.

This shifting cycle has implications for scientists' understanding of climate, evolution and even the development of the solar system itself.

Researchers probing Arizona's ancient rocks have found the first physical evidence of the cycle, long predicted by astrophysicists. The discovery was published this week in the journal Proceeding of the National Academy of Sciences.

This picture of planet Earth, taken from the International Space Station, shows Italy, the Alps, and the Mediterranean on January, 25, 2016. Tim Peake/Handout/NASA/Reuters

The team of scientists traced evidence for this cycle back some 215 million years—165 million years longer than mathematics alone can reliably predict. Beyond 50 million years, too many other factors get mixed up in the sums.

"This is truly complicated stuff," said study co-author Paul Olsen, a paleontologist at Columbia University, in a statement. "We are using basically the same kinds of math to send spaceships to Mars, and sure, that works. But once you start extending interplanetary motions back in time and tie that to cause and effect in climate, we can't claim that we understand how it all works."

Cores, not calculators

The research team analyzed 1,500-feet cores of rock from Arizona's Petrified Forest National Park and deep cores from suburban New York and New Jersey. The Arizona rock, which dates back from 209 million to 215 million years ago, is from the time of early dinosaur evolution.

The New Jersey and New York rocks don't contain the volcanic ash layers that can date them precisely, but the team believed they dated back to the same time window. The cores show that New Jersey and New York underwent alternating wet and dry periods. The team thought this might be a clue to the 405,000-year cycle.

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Although the team could only precisely date the Arizona cores, they did find evidence of polarity reversal—when the Earth's magnetic poles flip every 200,000 years or so—in both sets of rock.

Combining data from both sets of rock, the team picked out the 405,000-year cycle acting as a kind of master intensity dial for climate change. The cycle seemed to indirectly impact change—dialing up or dialing down the effects of shorter-term cycles.

Complicated cosmic gymnastics

Other cosmic gymnastics making Earth's climate swing include a shorter, 100,000-year orbital eccentricity and changes to the Earth's tilting, wobbling axis.

Known as "Milankovitch cycles," these can have a serious impact on the Earth's climate in the shorter term. Although scientists have shown they have driven climate flips from hot to cold a number of times over the last few million years, it is hard to pin down their effects.

Some may cancel each other out while others combine and lead to drastic changes, for example. The relationship between these cycles and greenhouse gases like carbon dioxide is also under debate.

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"There are other, shorter, orbital cycles, but when you look into the past, it's very difficult to know which one you're dealing with at any one time, because they change over time," said lead author Dennis Kent, an expert in paleomagnetism at Columbia University and Rutgers University, in the statement. "The beauty of this [405,000-year] one is that it stands alone. It doesn't change. All the other ones move over it."

Every 405,000 years, Kent and Olson said, seasonal differences become more intense as the orbit reaches its elliptical peak. Then, 202,500 years later, these differences calm down as the orbit becomes more circular.

These changes will have had a huge impact on ecological systems around the globe, influencing the evolution of life itself. Linda Hinnov, a professor at George Mason University who was not involved in the study, said the research could help scientists understand more about the evolution of dinosaurs, for example. The findings, she said, are "a significant new contribution to geology, and to astronomy."

Day to day, however, this giant orbital metronome won't have that much impact on us. "It's pretty far down on the list of so many other things that can affect climate on [time scales] that matter to us," Kent said.