14 DAY TRIAL // Due to which process can we observe perfectly horizontal layers on the limestone cliffs (lines that repeat rhythmically at similar distances upside down)?
The answer of the scientists: we should study the oscillations of the Earth's rotation axis. A kind of "Egg of Columbus", this explanation is accepted today, at least in principle. The chalk of some rocky cliffs is 90 million years old, each layer representing between 20 and 40,000 years of sedimentation. This periodicity would correspond exactly to the oscillations in the rotation axis of our planet.
At each 23,000 and 41,000 years, approximately, two types of oscillations are produced. Each oscillation, even if of low amplitude, triggers a modification of the geographical repartition of the solar energy receive by the Earth, provoking, alternatively, a spreading and a regression of the ice pack, so that the sea level varies, with a consequence on the differently colored layers of the cliffs of the marine shores, reflecting this rhythmic fluctuation.
The cliffs represent just one category of witnesses to the consequences of the "behavioral" changes of the Earth and its climate. The monsoon cycle, the deep current of the North Atlantic (that climbs on the surface on Antarctica), the dust winds crossing the Pacific, various sedimentary deposits from the currently dried great lakes reflect the power of the oscillation phenomenon of the world's axis.
The phenomenon is not only limited to the balance of the rotation axis.
Scientists detected that at each 100,000 years a variation of the eccentricity is produced, thus of the Earth's orbit around the Sun. This oscillation gives birth to a maximal difference of about 0.1 % of the total solar energy that we receive. This difference, apparently minimal, is still enough to change the climate of the whole planet, triggering glaciations.
Indeed, geological data show that the Ice Ages re-emerged at each 100,000 years in the last 800,000 years. There is a tight link between the amplitude of the eccentricity change and that of the glaciations.
This hypothesis was first emitted by the Serbian geophysicist Milutin Milankovici. But how can such weak variations be able to induce such important climate changes?
Most researchers believe it is a cumulative phenomenon. Increasingly cooler summers have as a consequence less melted snow, which can accumulate from one year to another, forming along the years ice packs and caps.