418 EARTH/Orbital Variation (Including Milankovitch Cycles) Figure Estimated changes in the obliquity and climatic precession periods related to a changing distance between Earth and the Moon over the past 440 My, according to calculations by Berger and Loutre in 1994 Note that the periods of obliquity and climatic precession change due to a change of the precession constant p, whereas the eccentricity periods remain unaffected Note that this diagram is for illustrative purposes only, and the exact variation of orbital frequencies over tens of millions of years is not yet known in detail Figure 10 Lithological magnetic susceptibility data from Leg 154 of the Ocean Drilling Program These data, analysed by Shackleton and colleagues in 1999, demonstrate the fidelity with which orbital variations can be encoded in the geological record The magnetic susceptibility parameter, plotted together with filters that extract the visible cycles, chiefly reflects variations between terrestrial (clay rich) and marine (carbonate rich) sediments, being forced by a dominant obliquity signal