"T. rex" and the Crater of Doom [Hardcover]

Ah, yes. Innocence. But 14-year-olds aside, this is a fascinating and delightful story of scientific discovery and triumph second to none. It can be compared to James D. Watson's The Double Helix: A Personal Account of the Discovery of the Structure of DNA, both in terms of the importance of the discovery and for bringing to the reader some of the excitement and adventure of the quest. It is not, however, as the title might imply, the reading equivalent of watching a Stephen Spielberg movie! And perhaps we can be thankful for that.

T. Rex and the Crater of Doom is the story of one of the great scientific discoveries of the twentieth century. Prior to Alvarez's work, it was not known what had caused the extinction of the dinosaurs. Volcanism, disease, climate change, etc., were put forward as possibilities. But in1970 Alvarez began to believe that a large meteor or a comet had struck the earth with enormous force causing the extinctions. But how to prove it? At first it wasn't even imagined how a meteor could bring about such a catastrophe; but gradually it was seen that the debris thrown into the atmosphere by the force of impact would encircle the earth and block out the rays of the sun for months or even years at a time, thereby killing off plants both on the land and in the sea, thereby collapsing the food chain and starving the dinosaurs and most other creatures.

This was the breakthrough idea, and an exciting idea it was. Of course there was great resistance, as there always is in science when established opinions are threatened, and Alvarez and his team of scientists had to fight mightily against the orthodoxy of uniformitarianism which had held sway in geology and paleontology since the time of Charles Lyell. It wasn't until twelve years later in 1992 that Alvarez's theory finally found general acceptance in the scientific community.

One of Alvarez's purposes in this book is to show a general readership how scientific discoveries are made and confirmed. His tone is generous and he goes out of his way (unlike Watson in The Double Helix) to give credit to everyone involved. He makes it clear that the work was a shared enterprise. One thing that stood out in my mind was the central contribution from Alverez's father, Luis, a physicist who unfortunately died before the theory could be confirmed.

Alvarez does however allow himself an occasional sarcasm vis-a-vis the old order. Characterizing the "conventional geologic opinion" on the formation of craters like the Meteor Crater in Arizona as due to "mysterious explosions that occurred at random times and places for no evident reason," he appends this observation: "In retrospect this causeless mechanism...is indistinguishable from magic, but at the time many geologists considered it preferable to catastrophic impacts." (p 76)

Science is especially subject to the braking effect of established opinion because it is extremely difficult for anybody to allow that the established beliefs of their entire professional career can suddenly be overturned. All your life you believed one thing and one day you wake up and some whippersnapper has overturned the entire edifice! That is hard to take, and so entrenched opinion wars against new discovery. But that is as it should be since extraordinary claims do indeed require extraordinary proof.

Therefore, just as "the course of true love never did run smooth" (Shakespeare), so it is with science. Alvarez recounts an early misdirection in the quest when it was thought that they had found plutonium-244 in the KT boundary clay, possibly indicating a nearby supernova explosion 65 million years ago. He and Frank Asaro took their discovery to Earl Hyde, a nuclear chemist who listened patiently to the details and then said, "Do it all over again." This was very good advice because when they did it all over again they found they had erred: there was no plutonium-244 in the clay samples! (p. 74)

After reading this book we are left with an intriguing question: what was the role of volcanism, not only in the KT extinction but in the Permian-Triassic as well? Alvarez hints that there must be more than coincidence involved in the fact that during both extinctions there is indisputable evidence of vast lava flows. Does a truly monstrous impact somehow trigger volcanic eruptions? An "intriguing mystery" is what Alvarez calls it. (pp. 143-144)

This book should be read in conjunction with David M. Raup's The Nemesis Affair: A Story of the Death of Dinosaurs and the Ways of Science which covers some of the same ground (especially the fight against established opinion) while claiming a 26-million year periodicity for impact extinctions caused by Oort Cloud perturbations from a hypothetical companion star, dubbed "Nemesis."

The explanation of Lyell, the father of uniformitarianism, for the faunal differences either side of the K/T boundary was that it was an unconformity. It marked a large time gap. But the author's work on polarity reversals had cut the K/T gap to less than half a million years, probably less than a hundred thousand years.

Iridium Anomalies

Discussion started with his father, Luis Alvarez, the Nobel Prize winning physicist, about how long a time period the boundary clay represented. The surrounding limestones contained 5 to 10 per cent clay. So was the clay layer deposited when limestone deposition stopped, in which case it represented several thousand years. Or was there a pulse of increased clay input? In which case it represented only a few years. How to do this? Use meteorite dust! (measured as iridium content). The assumption was that meteor dust falls constantly (in tiny amounts) and the amount of dust would tell you how long a bed took to deposit. So if it was deposited in a short time there would be no iridium and if it represented several thousand years there would be about 0.1 parts per billion. (There are about five billion people on earth, so detecting 0.1 ppb is equivalent to finding half a person out of the whole population of the earth.) The analysis was made and it was 9 ppb - 45 people instead of ½ a person! Why? Could it have been a supernova? - No, there was no plutonium in the clay. What could kill dinosaurs and foraminifera and leave iridium but no plutonium? Eventually the idea of a giant meteor impact and its associated dust cloud came to be the only contender.

In the meantime more iridium anomalies at the K/T boundary were found and more and more disciplines became involved. What had been the concern of geologists and palaeontologists, drew in chemists, mineralogists, geochemists, astronomers, physicists, meteorologists, ecologists, and statisticians. Geological problems rapidly became interdisciplinary ones.

Find the Crater

The main stumbling block to the acceptance of the impact theory was the lack of a crater. No visible crater was of the right size or date. Was it covered by sea or ice or had it been subducted? Spherules, thought to be derived from the target rock, were calcium and magnesium rich, indicating, at first glance, an oceanic (basalt, gabbro) origin. But no sub-sea craters were known. The easy option was to say it had been subducted and so had disappeared. And didn't need to be looked for.

Eventually the crater was pinpointed by looking for tsunami deposits. If an impact hit the sea (or, as it turned out, the land near the sea) it would cause tidal waves to radiate out. These would cause erosion of the sea floor at depths greater than normal wave base. As they approached the shore they would trigger turbidites to flow down slope. So the search was on for torn up sea bed covered by sedimentary debris, right at the K/T boundary. And preferably with spherules. These would be found round the ocean where the impact occurred.

These deposits turned up around the Gulf of Mexico and the Caribbean. And soon the crater was pinpointed to Chicxulub on the Yucatan peninsula. This was close to the sea but was not on oceanic crust. The limestone and dolomite of the site had provided the Ca and Mg which had suggested an oceanic target and so confused the search.

Read the Book!

I hope that this review encourages you to read the book. The story is exciting - Death of the Dinosaurs, Comet Crashing into the Earth, "Nuclear" Winter, Will it Happen Again? - and gives the flavour of research. It is extremely complicated but the author has a very firm grasp on his material and is not afraid to explain both the simplest and most complex of concepts.

He makes the point that geology is an interdisciplinary science. Other sciences are reductionist, simplifying things so that they can be understood. Geology puts these components back together so that the Earth can be understood.