The 30th Ockham Lecture - 'Life’s a Beach: the Moon, the Tides, and the Emergence of Terrestrial Vertebrates'

Date: Monday 3 June 2019
Time: 17:00 - 19:00
TS Eliot Theatre, Merton College

Given by Professor Steven Balbus FRS, Savilian Professor of Astronomy and Head of Astrophysics at the University of Oxford.

The lecture was introduced by Professor Alex Schekochihin and was followed by a Q&A session.


The very similar angular sizes of the Sun and Moon as subtended at the Earth are generally portrayed as coincidental. Is it possible that there is some science behind this odd fact? Close angular size agreement is a direct and inevitable mathematical consequence of even roughly comparable lunar and solar tidal forces. I will argue that the latter was a biological imperative for the evolution of land vertebrates and can thus be understood on the basis of anthropic arguments. Comparable tidal forces from two astronomical sources lead to spring and neap tides. This appearance of what must be an unusual planetary tidal pattern is consequential for the palaeogeography and biology of the Late Devonian period. Two great land masses were separated by a broad opening tapering to a very narrow, shallow-sea strait. The combination of this geography and variable tidal forces would have been conducive to forming a rich inland network of shallow, very transient tidal pools, leading to an epoch when shallows-loving fish were forced to acquire land navigational skills for survival. I will discuss the recent fossil evidence showing that important transitional species lived in habitats strongly influenced by intermittent tides, and speculate on the role of tides in the late Devonian mass extinctions.

Watch the lecture

The Ockham Lecture Series

The Merton College Physics Lecture (the Ockham, or Occam, Lecture, so named in honour of one of the greatest—if unattested—alumni of the College and of his philosophical principle of intellectual discipline) started in 2009 and is held once a term. It is organised by the physics tutors of the College to promote both intellectual curiosity and social cohesion of the Merton Physics community.

Attendance is by invitation: All Merton physicists (and sympathisers!) belonging to the three Common Rooms (JCR, MCR and SCR) are invited, as are the Old Members. Their guests are also accommodated, space permitting.