EARTH/Orbital Variation (Including Milankovitch Cycles) 419 Figure 11 (Top) Evolutionary spectrum (frequency vs age, amplitude colour coded) of Ocean Drilling Program Leg 154 lithological data (combined magnetic susceptibility and colour reflectance) (cf Figure 10) These data, analysed by Shackleton and colleagues in 1999, and contrasted to astronomical calculations of Earth’s orbital variations, demonstrate that the geological data contain an imprint of long term amplitude modulations of astronomical forcing components (Bottom) The astronomical solution provided by J Laskar geological time-scales Laskar found that the calculations of orbits diverge exponentially with time for a given set of initial conditions This implies, for example, that if the present position of a planet is known with a relative error of $10 10, this error increases to $10 after 10 My, and reaches the order of after 100 My Despite these limitations, the determination of astronomical parameters, such as the planetary masses, velocities, and positions, is improving due to additional satellite measurements