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School of Physics and Astronomy

An Astrophysical View of the Emergence of Terrestrial Vertebrates

6 November 2015

Time: 2:30pm
Venue: GO Jones Room 610

Astronomy Unit Seminars
Steve Balbus
Richard Nelson

The very similar angular sizes of the Sun and Moon subtended at the Earth is generally portrayed as coincidental.  In fact, close angular size agreement is a direct mathematical consequence of even roughly comparable lunar and solar tidal amplitudes.   I will argue that the latter was a biological imperative.  Comparable tidal amplitudes, sharing close but distinct frequencies, leads to beats and strongly modulated forcing.  This tidal pattern must be understood in the context of paleogeographic reconstructions of the Late Devonian period.  Two great land masses were separated by a broad opening tapering to a very narrow, shallow-sea strait. A classic WKB wave analysis suggests that the combination of this geography and modulated tidal forces would have been conducive to forming a rich inland network of shallow but transient tidal pools at an epoch when fishy tetrapods were evolving.  I will discuss the fossil evidence showing that important transitional species lived in habitats strongly influenced by intermittent tides. When the waters became anoxic, perhaps from sustained in wash of organic debris, one of the great mass extinctions ensued. The tetrapods were among the few of their line that endured, and we are their legacy.