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The Sciences

A Catastrophic Career

The LoomBy Carl ZimmerNovember 23, 2008 4:49 AM


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Last night I strapped on a bow tie and shot out my tuxedo cuffs, got in the car, and headed to the upper West Side to celebrate a global cataclysm. Actually, I was helping to celebrate the geologist who discovered the cataclysm. Walter Alvarez was receiving the Vetlesen Prize, the highest honor in the earth sciences. Under the magnificent rotunda at Columbia's Low Library, we sat down to dinner. Michael Purdy, the director of Columbia's Lamont-Doherty Geological Observatory, kicked off the event by explaining that Alvarez was winning the award because he had changed the way earth scientists view the history of the Earth. Later, Columbia president Lee Bollinger got up to present him with the award, declaring that Alvarez had shown how life was intimately connected to the cosmos. The real highlight of the evening, however, was listening to Alvarez himself. He described growing up in northern California, where the violence of the San Andreas fault contrasted with the gentle climate. Then he went to Carleton College in Minnesota, where the geology was gentle and the weather was violent (he was reminded the glaciers were not long gone). Alvarez likened the cold winters he spent there to the icebound winter in which geology was trapped in the 1950s. The science was stuck in two dogmas: the fixity of continents and the total domination of uniformitarianism--the idea that all geological features on Earth were created by the same processes we see today, like erosion and slow uplift. Alvarez would go on to watch the first dogma fall apart, and then help attack the second. Alvarez started grad school in 1962 at Princeton, where a number of geologists were amassing evidence that the continents were not fixed, but instead were gliding around the Earth and crashing into each other like bumper cars. Alvarez began to study the geology of Italy, trying to figure out how lots of little plates of crust joined together to produce Europe's boot. He and his colleagues would spend long days hiking the Appenine mountains, and unwind in little restaurants in the evening. He referred to his field work as geograstonomic excursions. (Alvarez, an excellent writer, has just published a book on the geology of Italy, called The Mountains of St. Francis.) Among the formations in the Appenines are rocks that span the end of the Cretaceous Period and the beginning of the Paleocene, some 66 million years ago. In 1977 Alvarez took a sample of the rock to his new job at Berkeley, and with the help of his father, physicist Luis Alvarez, he measured a rare element called iridium in the rock. Alvarez wanted to use the iridium, which sprinkles down from space, as a clock to measure how quickly layers of rock had formed. But then they discovered the layer at the very end of the Cretaceous was loaded with iridium--far more than the rocks directly below and above. Alvarez and his colleagues proposed that a gigantic comet or asteroid had smashed into the Earth, delivering the spike of iridium he had measured. They also argued that the impact did something else: it triggered the mass extinctions that claimed the big dinosaurs (but spared the feathered dinosaurs alive today). This idea, Alvarez told us, flew in the face of uniformitarianism. And when the crater formed by the impact was discovered in Mexico in the 1990s, Alvarez said that hard-core, absolutist uniformitarianism was dead. Today, Alvarez declared, geologists see the history of the planet as a mix of uniformitarian changes and catastrophic events like impacts. I'm no historian of science, but I think Alvarez was pretty much on the money. But his legacy is more complicated than a lot of people seem to think. The case file on the mass extinctions 66 million years ago is not closed. No one now denies that a massive hunk of rock landed on the planet, or that it triggered tidal waves and all sorts of climate mischief. But there's some debate about whether it alone caused all the extinctions from that time. Massive volcanoes were mucking up the atmosphere in India at around the same time. Some extinctions seem to have occurred hundreds of thousands of years after the impact. Some researchers argue that dinosaurs were already in a steady decline for millions of years when it hit. When Alvarez's impact was confirmed, some scientists began to argue that evolution was driven by regular impacts over the history of life--perhaps every 20 million years or so. But other than the end of the Cretaceous, there's no compelling evidence at the moment for any impact coinciding with a pulse of extinctions. On the contrary--big impacts often appear to have had little effect on the global diversity of life. Still, catastrophic change looks to be important for triggering extinctions. It's just that Earth may not need any help from space to wipe out millions of species. I wrote about this at length in my foreword to the 2008 edition of Alvarez's book, T. rex and the Crater of Doom. (You can read it on my web site.) When I turned in my foreword, I was a little nervous. Alvarez, after all, would be given a chance to read it. But instead of blowing his stack, Alvarez was pleased with it and offered some fact-checking corrections on the details. It didn't bother him to see science move forward--he just wanted to help give a push. (I've now got his autograph on my copy of the book.) Alvarez brought his speech to an end, declaring that now it is autumn (he's 68). He was grateful to have been a part of geology's change over the past 40 years. Perhaps, he suggested, it was a good time to breathe in the cool air of November--to go to an Italian restaurant in the Appenine mountains and her an old Italian song geologists like to sing in the evening. He smiled, a little teary, and stepped down as his fellow geologists stood and applauded. I'm not so sure that Alvarez is that deep into autumn, though. Purdy mentioned that it took a week to contact him to let him know he'd won the prize. At the time, Alvarez was far out of cell phone range, deep in the mountains, communing with rocks. [Image: PNAS]

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