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Night Comes To The Cretaceous


Night Comes To The Cretaceous, James Lawrence Powell, Freeman, 1998, ISBN 0-7167-3117-2


This book is the latest retelling of the saga of the Dinosaur Killer, the Asteroid of Doom, one of the great scientific detection stories of the century and one which has broad implications for evolutionary theory.

The story has been told many times. I have on my shelves three other popular science accounts:

The Great Dying by Kenneth Hsu (1986)
The Nemesis Affair by David Raup (1986)
T-Rex and the Crater of Doom by Walter Alvarez (1997)

Alvarez (p156) devotes most of a page in the notes to listing major accounts of the story, included Officer & Page's diehard defenses of the vulcanism theory. Powell has prolific references in his footnotes but no reading list which I count as a fault.

Powell takes an unusual approach in his account; he treats it as a case example in applying the scientific method according to the Popperian schema. The discovery of the Iridium spike in the K-T boundary clays and the formulation of the K-T impact extinction theory is presented. The Alvarez hypothesis is broken into two parts, the impact hypothesis and the extinction hypothesis. For each half major predictions are listed and major possible falsifications are listed. The search for confirming evidence for the predictions and the falsifications is described.

The effect is a bit like cookie-cutter science; however the approach has its merits. It clarifies what the major issues were (and are). In particular part III (was there a sudden extinction) vividly illustrates how difficult paleontology really is. One of the tangential benefits of the affair was the illumination of the deficiencies of the paleontological record and the difficulties of making solid inferences. A key issue was whether the dinosaurs had been dying out in the last era of the Cretaceous or whether they had maintained diversity right up to the very end. It became clear that this question was much harder to answer than had been realized. Indeed it is still open to debate.

A fault of Powell's approach is that it makes the process seem simpler than it is. We are trying to reconstruct events that took place a very long time ago. There are only scattered and minute traces of those events. The inferences by which we reconstruct those events are subtle and indirect and subject to multiple interpretations. Most of the evidence is missing; it is easy to draw erroneous conclusions because particular bits of data are not representative. It is to Powell's credit that he does make the difficulties clear.

One of the unfortunate features of the affair is that it lends itself all too readily to a melodramatic account of the good impact theorists versus the bad uniformitarians. Given the acrimonious history of the debate in the journals one can scarcely avoid giving an account in terms of a rousing good fight. The temptation, however, is over dramatize the conflict and under play the scientific issues in question. Powell does not entirely escape this temptation.

As a side note one of the merits of the book is that it gives a good sense of how utterly devastating the K-T asteroid strike was. It is one thing to say that 70% of all species (including all of the dinosaurs) went extinct. Seventy percent doesn't sound too bad; it is another thing to say 99.99% of all life died. Almost everything living thing on the face of the Earth died either immediately or shortly thereafter. The impact was a Richter 13 event. Powell does a good job of bringing the scope of devastation to life or, rather, to death.

The last part of the book deals with some of the larger implications. Are major extinctions driven by major impacts? Is there a periodicity in these impacts? Are impacts the major cause of large scale evolutionary change, the forcing function? These questions are very open; they do not yet lend themselves to the pat hypothesis/prediction/fabrication schema. In the conclusion of the book Powell remarks that the last few decades have been a golden age of geology; we have discovered that there are very important things (plate tectonics, impact catastrophes) that we didn't know about that have changed our picture of the history of Earth drastically.

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