Atmosphere/Earth interaction and Earth rotation at geological timescale

The length-of-day (i.e. the time of one rotation of the Earth) is deeply affected by the interaction of the Earth with the atmosphere, and consequently by the state of the atmosphere and by the climate. At very long timescale, the climate has changed deeply, due to the change of the paleogeography, to the formation/melting of icecaps, to the change of the CO2 content of the atmosphere... Those climate changes have impacted the mean rotation state of the atmosphere, which in return change the length-of-day. By analysing the outputs of more than 200 climate models of the past Earth, we have separated the effects from the CO2 changes from those of the paleogeography, and those from the ice-caps. This allows to identify the changes in the atmosphere dynamics of the different cause, and their signature in the Earth rotation.