Environment

Rock-solid evidence shows how Earth's eccentric orbit affects climate change

Researchers have found rock-solid evidence for a 405,000 year cycle in Earth's orbit, which affects climate change
Researchers have found rock-solid evidence for a 405,000 year cycle in Earth's orbit, which affects climate change
View 5 Images
The researchers drilled rock cores from the Petrified Forest National Park in Arizona
1/5
The researchers drilled rock cores from the Petrified Forest National Park in Arizona
The researchers were able to date the rock cores by analyzing isotopes in layers of volcanic ash, as well as through clear signals left during magnetic pole reversals
2/5
The researchers were able to date the rock cores by analyzing isotopes in layers of volcanic ash, as well as through clear signals left during magnetic pole reversals
Rock cores drilled from Arizona gave vital clues to how long-term cycles in Earth's orbit affect climate change
3/5
Rock cores drilled from Arizona gave vital clues to how long-term cycles in Earth's orbit affect climate change
Dennis Kent with one of the Arizona rock cores
4/5
Dennis Kent with one of the Arizona rock cores
Researchers have found rock-solid evidence for a 405,000 year cycle in Earth's orbit, which affects climate change
5/5
Researchers have found rock-solid evidence for a 405,000 year cycle in Earth's orbit, which affects climate change

You probably picture the Earth's annual journey around the Sun as being more or less a circle, but that's only true some of the time. Models have long suggested that our home planet's orbit shifts from circular to elliptical and back again over hundreds of thousands of years, which plays a part in natural climate swings. Now, scientists have found the first physical evidence for the cycle, and traced it back to before the dinosaurs.

The Earth goes through regular, large-scale cycles of ice ages and warmer periods, driven by a whole range of factors. Some of the main contributors are what are known as Milankovitch Cycles, along with variations in the Earth's orbital path (cycling every 100,000 years), its axial tilt (on a 41,000-year cycle) and the "wobble" of its spin (on a 23,000-year cycle). These affect how much solar energy hits the Northern Hemisphere at different times of the year, and in turn affect the planet's long-term climate.

But scientists have long suspected another, much longer cycle sits over the top of them. Every 405,000 years or so, the shape of the Earth's orbit shifts from almost perfectly circular to slightly elliptical, thanks to the complex interactions between Earth and other planets, particularly our closest neighbor Venus and the huge gravitational influence of Jupiter. This has been traced back about 50 million years, but with so many moving parts it all gets a bit murky the further back you look.

"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," says Dennis Kent, lead author of the study. "The beauty of this one is that it stands alone. It doesn't change. All the other ones move over it."

The researchers were able to date the rock cores by analyzing isotopes in layers of volcanic ash, as well as through clear signals left during magnetic pole reversals
The researchers were able to date the rock cores by analyzing isotopes in layers of volcanic ash, as well as through clear signals left during magnetic pole reversals

Previously, this longer cycle has been hypothesized based on calculations of the movements of planets, but now researchers from Columbia University and Rutgers University have found the first physical evidence for it. The team drilled rock cores 1,500 ft (457 m) deep from the Petrified Forest National Park in Arizona, and compared them to similar deep cores from New York and New Jersey.

By analyzing the decay of isotopes in layers of volcanic ash dotted through the rock, the team was able to date the Arizona cores back between 209 and 215 million years ago. That places them in the late Triassic, around the beginning of the age of the dinosaurs. The researchers were also able to see clear signs of magnetic field reversals, a fairly regular cycle where Earth's magnetic poles flip every 200,000 to 300,000 years.

The researchers compared the Arizona cores to those from New York and New Jersey, and lined up the points of pole reversals. Combining both sets of data also showed that they formed at the same time and had similar characteristics that pointed to the influence of a longer-term cycle.

The cycle reared its head in the rocks in the form of alternating, extreme wet and dry periods. Darker layers indicate black shale, formed at the bottom of deep lakes as a result of wetter seasons, while lighter-colored rock indicates much drier conditions. These conditions cycled through every 405,000 years, with the darker/wetter times suggesting the Earth was in a highly-eccentric orbit, while the lighter/drier times represent a smoother, circular path.

The researchers say that this larger-scale cycle doesn't directly affect the Earth's climate – instead, it either strengthens or weakens the effects of the smaller Milankovitch Cycles.

The researchers drilled rock cores from the Petrified Forest National Park in Arizona
The researchers drilled rock cores from the Petrified Forest National Park in Arizona

"It's an astonishing result because this long cycle, which had been predicted from planetary motions through about 50 million years ago, has been confirmed through at least 215 million years ago," says Kent. "Scientists can now link changes in the climate, environment, dinosaurs, mammals and fossils around the world to this 405,000-year cycle in a very precise way."

The research was published in the journal Proceedings of the National Academy of Sciences.

Sources: Rutgers University, Columbia University

12 comments
f8lee
Well now I'm waiting for Al Gore to fill me in on why human activity is to blame for all that is going on! I mean, it must be Homo sapiens' fault that these nasty perturbations have made the earth wobble so.
MikeVidal
I have been saying for years that the perturbations in the earths orbit and its axis tilt, along with the variability of the suns output has a much greater effect on our climate than man. This just vindicates what I have been saying.
The Bishop of D
The meaning of stability is different for self organizing nonlinear dynamic systems than for linear systems. A stable self organizing nonlinear dynamic system oscillates between limits (the Lorentz, or "butterfly" strange attractor is an excellent example).
McDesign
No - I thought anthropogenic effects were the only things that affected climate. Are you telling me there are more? Crazy, man!
Grunchy
Why are we wasting time looking at other things when we need to focus on devastating our energy industries? First things first ! We can look at geo mechanical effects later.
guzmanchinky
We still need to get rid of fossil fuels.
pryor
Cue the climate change deniers yapping about how this proves that human activity isn't causing the effects of climate change. Really? Folks, try reading the article carefully -- like the part about how "this longer cycle has been hypothesized based on calculations of the movements of planets" -- and you'll find that this isn't a new wrinkle in the calculation of climate models.
Gary Kerkin
Pryor you shouldn’t “cherrypick” the information. By all means quote from the article but, please, if you are quoting to make a point ensure that you quote the complete thing. Yes, the cycle was hypothesised, but the author of the article wrote: “Previously, this longer cycle has been hypothesized based on calculations of the movements of planets, but now researchers from Columbia University and Rutgers University have found the first physical evidence for it.” This is the essence of science: form a hypothesis, find a method of investigating it, collect data by the methodology, then accept or reject the hypothesis based on the results. This study looks like the first step in establishing the presence of a longer Milankovich cycle.
Nik
The Earth orbits the sun, but the sun orbits the centre of the galaxy, and at regular 150 million year intervals, the solar system passes through the arms of the galaxy. When it does, interstellar dust in the arms attenuate the suns radiation reaching Earth. This usually causes a major ice age, that can last for millions of years. The Earth is in one of these now! The climate has been steadily cooling for the last 30 or so million years. This inter ice age, is the coldest it has been since the Permian Extinction, some 270 million years ago, and also has the lowest level of Atmospheric CO2, in spite of claims to the contrary by the carbon tax scammers. This 'galaxian ice age' could be a repeat of the one that ended 600 million years ago, when the Earth became a 'snowball' for about 100 million years. Here's a link to a graph showing the climate for the last 600 million years. http://www.geocraft.com/WVFossils/PageMill_Images/image277.gif The 150 million year cold periods are very clear. Malenkovitch cycles are superimposed on these galaxy induced events. Also the path of the solar system is not in the plane of the galaxy, but follows a sinusoidal path passing through the plane at around 30 million years intervals. This also caused climatic changes.
Old J Hawthorne
Whether by human intervention or not, climate change is just one problem, and it's not going to change anytime soon. What we can do is disrupt the cycle of countries that routinely dump garbage in the oceans and try to do something about the garbage that is already there...and there are other problems we can actually do something about. Changing to LED light bulbs, for instance, will not make any difference to the climate.