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Earth’s Orbit Varies From Nearly Circular to Slightly Elliptical Over 405,000 Year Cycle


Research reported in the Proceedings of the National Academy of Sciences (sorry, but everything except the abstract is behind a paywall) has confirmed that the Earth’s orbit varies over a 405,000 year cycle influenced by the masses of Jupiter and Venus, which takes it from a nearly circular orbit to a slightly elliptical orbit around the sun.  Currently, the Earth is in a nearly circular orbit.

The research was based on evaluation of lead-to-uranium ratios in a core drilled from rock in the Petrified Forest National Park in Arizona.  The core went back nearly 250 million years (give or take a few tens of millions) and far exceeded the length of previous cores– the maximum was 50 million years.

The New York Times reported that previous cores in the Northeast, 2,000 miles away, showed reliable climate cycles of 202,500 years but were unsuitable for determining uranium-to-lead ratios.

The new core will be a big help in dating fossils back to 250 million years ago, which just happens to be right after the worst disaster in Earth’s history (suspected but not proved to be due to runaway volcanism which produced the enormous lava fields known as the Deccan traps) and around the time the first dinosaurs and mammals appeared.

(photo courtesy of

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