The rotation of the Earth impacted by the movement of the continents and the climate?

The Earth revolves on itself and around the Sunbut these movements are not simple. Indeed, theorbit earth is far from being a perfect circle and is more like an ellipse. Likewise, the axis of rotation of our Planet is not fixed. It oscillates slightly and very slowly, over a period of approximately 25,679 years, a bit like a spinning top about to stop. These two parameters, ellipticity and precession of the equinoxes, modulate the Earth’s climate on large time scales.

Precession, in particular, varies the amount of solar radiation impacting the Earth’s surface (sunstroke). Understanding the evolution of this parameter is therefore important to better qualify the climatic changes that have occurred over time. Because it is indeed a variable parameter. The precession of the Earth’s axis is in fact governed by the forces of attraction exerted by the Moon and the Sun on Earth and who are responsible for the tides. Tidal effects, however, depend on Earth-Moon distance and the ellipticity of Earth’s orbit.

Sediments, archives of orbital parameters

Over geological time, these different parameters have undergone variations. If there are theoretical models allowing the evolution of these orbital parameters to be predicted over time, it is however not easy to find traces of them in the terrestrial natural archives.

Two scientists have looked into this question. In an attempt to observe the evolution of the period of the precession of the Earth’s axis, they were interested in the information contained in the sediments. Sedimentary deposits are in fact sensitive to variations in the environment and make it possible to trace the environmental conditions that prevailed during their formation. This is how we observe, in the sedimentary series, great cyclical variations linked to the climate and in particular to the changes in ice volume : Those are the Milankovitch cycles. However, these cycles are intimately linked to the orbital parameters that are theeccentricitythe tilt and precession of the Earth’s axis.

In an article published in Global and Planetary Change, two researchers present the results of their analyzes of sediment samples dating from the early Eocene (55.8 to 40.9 million years). From the study of Milankovich cycles, they were thus able to calculate “observed” precession rates which they compared with theoretical models of astronomical origin. While the values ​​generally agree for the age of 42.5 million years, this is not at all the case for the age of 55 million years. This discrepancy between the observed values ​​and the theoretical model raises questions.

Earth’s rotation affected by climate and geodynamics

For the scientists, it appears that certain parameters capable of influencing the precession of the axis are not taken into account in the theoretical model. But which ones?

To identify them, it is necessary to look more precisely at this period of the beginning of the Eocene. Because 55 million years ago, the Earth experienced several major upheavals. Firstly, climatic: this period is in fact marked by what is called a climatic optimum, characterized by globally very high temperatures and the absence of ice caps at the poles.

Secondly, geodynamics: it was at this time in particular that the collision between India and Asia began, and that the expansion of the ocean floor accelerated. For the scientists, this climatic and geodynamic situation could have influenced the tidal effects, which would then have been weaker than those predicted by the theoretical model. The convection mantle, in connection with surface plate tectonics, could also have influenced the ellipticity of the Earth’s orbit. All of which combine to affect the rate of precession.

This study shows the influence that can have earth dynamicsboth from the climatic point of view and from the internal processes, on orbital phenomena such as the precession of the axis.