Investigations into the impact of astronomical phenomena on the terrestrial biosphere and climate

TL;DR

This thesis investigates how astronomical phenomena influence Earth's biosphere and climate, finding limited evidence linking solar motion to extinctions or cratering, but highlighting Earth's obliquity variations as key in glaciation cycles.

Contribution

It provides a comprehensive Bayesian analysis of astronomical impacts on Earth's history, clarifying the roles of solar motion, galactic tides, and Earth's obliquity in climate and extinction events.

Findings

No clear link between solar motion and mass extinctions.

Galactic tides and solar orbit do not significantly affect impact cratering rates.

Earth's obliquity variations are primary in triggering deglaciations.

Abstract

This thesis assesses the influence of astronomical phenomena on the Earth's biosphere and climate. I examine in particular the relevance of both the path of the Sun through the Galaxy and the evolution of the Earth's orbital parameters in modulating non-terrestrial mechanisms. I build models to predict the extinction rate of species, the temporal variation of the impact cratering rate and ice sheet deglaciations, and then compare these models with other models within a Bayesian framework. I find that the temporal distribution of mass extinction events over the past 550 Myr can be explained just as well by a uniform random distribution as by other models, such as variations in the stellar density local to the Sun arising from the Sun's orbit. Given the uncertainties in the Galaxy model and the Sun's current phase space coordinates, as well as the errors in the geological data, it is not possible to draw a clear connection between terrestrial extinction and the solar motion. In a separate study, I find that the solar motion, which modulates the Galactic tidal forces imposed on Oort cloud comets, does not significantly influence this cratering rate. My dynamical models, together with the solar apex motion, can explain the anisotropic perihelia of long period comets without needing to invoke the existence of a Jupiter-mass solar companion. Finally, I find that variations in the Earth's obliquity play a dominant role in triggering terrestrial deglaciations over the past 2 Myr. The precession of the equinoxes, in contrast, only becomes important in pacing large deglaciations after the transition from the 100-kyr dominant periodicity in the ice coverage to a 41-kyr dominant periodicity, which occurred 0.7 Myr ago.