When looking at the orbits of moons around Jupiter and Saturn we often see what are known as resonances. For example, Jupiter's moon Europa takes twice as long to orbit as its neighbor Io, so that every second time Io gets back to the same spot, Europa is tugging at it. Cumulatively, this can change a moon's, or indeed a planet's, orbit.
Such ratios are not always permanent, however, and Meyers concludes that a change he found in the period of shifts between shale and clay is a result of a “resonance transition”, where Earth and Mars moved from one resonance pattern to another. At around 85-87 million years ago, Meyer found the cycle of Earth's orbital eccentricity shifted from 1.2 million years to 2.4 million years. Meanwhile, other orbital characteristics stayed the same. Such a change is the signature of a resonance transition with another planet.
Theoretical models of the evolution of the orbits of the planets suggest they should behave chaotically. This doesn't mean that the planets should bounce around like billiard balls after a break, but that small variations can lead to changes to their orbits that cannot be predicted over long periods of time, in this case anything over 50 million years. These models indicate that there should have been times where the planets moved from one resonance to another, with accompanying effects on the climate.
Although the idea of chaotic orbits dates back to 1989, previous geological evidence has been ambiguous. Meyer has claimed his findings, “Made possible by the availability of high-quality, radioisotopic dates and the strong astronomical signal preserved in the rocks" represent the clarity that has been needed to confirm the theory.