Cretaceous Cycles (image) University of Wisconsin-Madison Share Print E-Mail Caption The layer cake of sedimentary rock near Big Bend, Texas, shows the alternating layers of shale and limestone characteristic of the rock laid down at the bottom of a shallow ocean during the late Cretaceous period. The rock holds the 87 million-year-old signature of a 'resonance transition' in the orbits of Mars and Earth, definitive geologic evidence that the orbits of the planets in our solar system behave differently than prevailing theory, which held that the planets orbit like clockwork in a quasiperiodic manner. Credit Bradley Sageman, Northwestern University Usage Restrictions None 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.