Ancient Cycle (image) The Earth Institute at Columbia University Share Print E-Mail Caption Within ancient rocks in Arizona's Petrified Forest National Park, scientists have identified signs of a regular variation in Earth's orbit that influences climate. Here, one of the authors near the research site. Credit Kevin Krajick/Lamont-Doherty Earth Observatory Usage Restrictions Credit must be given. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.