Palaeontologists have traditionally tried to date the tree of life using the fossil record, which is patchy owing to the differentially preserved rock layers, the reworking of these layers by geological processes and the varying fossilization potentials of the organisms. These problems become especially acute for the most ancient scions in the tree of life. However, new fossils found in the Archaean and Hadean are constantly being described and reinterpreted, leading to a fluctuating timescale which does not allow for the analysis of evolutionary hypotheses. This thesis approaches this issue by synthesising knowledge from the fossil record and molecular dating strategies and produces a robust timescale for the tree of life. I used genetic data from extant organisms in the Eubacteria, Archaebacteria and Eukaryota. Dating the origin of these lineages and the last universal common ancestor (LUCA) required application of methods over greater timescales than they are normally applied to. It also includes the use of recently developed approaches, such as the fossilized birth death process and cross bracing, where restrictions are applied such that multiple nodes of a tree simultaneously evolve, as in the same speciation event in a dated gene tree. The combined approach of fossil calibrations can molecular clock methodology dates the origin of lineages more accurately. The results of this thesis show that life shares a common ancestor with an age close to the that of the Earth. A lag follows before the origin of the two domains, Archaebacteria and Eubacteria in the Archaean. Crown eukaryotes appear much later in the Proterozoic. These ages show that life evolves prior to the oldest known fossils. As reconstructed timelines improve, they can help us to elucidate more about the evolution of life and the changing world which it both inhabits and influences.
|Date of Award||24 Mar 2020|
- The University of Bristol
|Supervisor||Davide Pisani (Supervisor) & Philip C J Donoghue (Supervisor)|