Last updated May 15, 2018 at 10:17 am
While CO2 emissions are behind the global climate change that is currently focusing global thought, there is also a rather more subtle impact going on in the background
Gravitational tugs from Jupiter and Venus slightly elongate Earth’s orbit. Credit: iStock
Scientists drilling deep into ancient rocks in the Arizona desert say they have documented a gradual shift in the Earth’s orbit that repeats regularly every 405,000 years, playing a role in natural climate swings.
Gravitational tugs from Jupiter and Venus slightly elongate Earth’s orbit in an amazingly consistent pattern that influences our climate and allows scientists to more precisely date geological events like the spread of dinosaurs.
“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,” said Professor Dennis V. Kent, from the Department of Earth and Planetary Sciences at Rutgers University-New Brunswick.
“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.”
Earth’s magnetic field
Kent and colleagues linked reversals in the Earth’s magnetic field – when compasses point south instead of north and vice versa – to sediments with and without zircons (minerals with uranium that allow radioactive dating) as well as to climate cycles.
Dennis Kent with part of a 520 metre rock core from the Chinle Formation in Petrified Forest National Park in Arizona. Credit: Nick Romanenko/ Rutgers University-New Brunswick
“The climate cycles are directly related to how the Earth orbits the sun and slight variations in sunlight reaching Earth lead to climate and ecological changes,” he said.
“The Earth’s orbit changes from close to perfectly circular to about five per cent elongated, especially every 405,000 years.”
The work was carried out in the Newark basin, a prehistoric lake that spanned most of New Jersey, and in sediments with volcanic detritus including zircons in the Chinle Formation in Petrified Forest National Park in Arizona.
The team collected a core of rock from the Triassic Period, some 202 million to 253 million years ago. The core is 2.5 inches in diameter and about 1,700 feet long, Kent said.
Astronomical pattern
The results showed that the 405,000-year cycle is the most regular astronomical pattern linked to the Earth’s annual turn around the sun.
Prior to this study, dates to accurately time when magnetic fields reversed were unavailable for 30 million years of the Late Triassic. That’s when dinosaurs and mammals appeared and the Pangea supercontinent broke up. The break-up led to the Atlantic Ocean forming, with the sea-floor spreading as the continents drifted apart, and a mass extinction event that affected dinosaurs at the end of that period, Kent said.
Should we be concerned about all this? Probably not, says Kent, because it’s “pretty far down on the list of so many other things that can affect climate on times scales that matter to us”.
“On the other hand, all the CO2 we’re pouring into the air right now is the obvious big enchilada. That’s having an effect we can measure right now.
The paper was published in the Proceedings of the National Academy of Sciences.
