Scientists have long posited that periodic swings in Earth’s climate are driven by cyclic changes in the distribution of sunlight reaching our surface.
Scientists have long posited that periodic swings in Earth’s climate are driven by cyclic changes in the distribution of sunlight reaching our surface. This is due to cyclic changes in how our planet spins on its axis, the ellipticity of its orbit, and its orientation toward the sun — overlapping cycles caused by subtle gravitational interplays with other planets, as the bodies whirl around the sun and by each other like gyrating hula-hoops.
But planetary paths change over time, and that can change the cycles’ lengths. This has made it challenging for scientists to untangle what drove many ancient climate shifts. And the problem gets ever more difficult the further back in time you go; tiny changes in one planet’s motion may knock others’ askew — at first slightly, but as eons pass, these changes resonate against each other, and the system morphs in ways impossible to predict using even the most advanced math. In other words, it’s chaos out there. Up to now, researchers are able to calculate the relative motions of the planets and their possible effects on our climate with reasonable reliability back only about 60 million years — a relative eyeblink in the 4.5 billion-plus life of Earth.
This week, in a new paper in the Proceedings of the National Academy of Sciences, a team of researchers has pushed the record way back, identifying key aspects of the planets’ motions from a period around 200 million years ago. The team is led by geologist and paleontologist Paul Olsen of Columbia University’s Lamont-Doherty Earth Observatory. Last year, by comparing periodic changes in ancient sediments drilled from Arizona and New Jersey, Olsen and colleagues identified a 405,000-year cycle in Earth’s orbit that apparently has not changed at all over at least the last 200 million years — a kind of metronome against which all other cycles can be measured. Using those same sediments in the new paper, they now have identified a cycle that started out lasting 1.75 million years, but is now operating every 2.4 million years. This, they say, allows them to extrapolate long-term changes in the paths of Jupiter and the inner planets (Mercury, Venus and Mars), the bodies most likely to affect our own orbit.
Read more at Earth Institute at Columbia University
Image: This is geologist Paul Olsen at Arizona's Petrified Forest National Park, where 200 million-year-old rocks are helping reveal the long-ago motions of other planets. (Credit: Kevin Krajick/Earth Institute, Columbia University)
