Not only have the advances since the Alvarez theory appeared brought about a transformation of geology, they have greatly illuminated the role of chance in our solar system. We see that not only the death of the dinosaurs, but our presence on the earth, is contingent on the particular way in which the solar system originated and evolved. The K-T impact was set in motion nearly 4.5 billion years ago with the birth of the solar system. From that primordial chaos arose a comet or an asteroid that through the subsequent eons was intermittently pounded by impact and continually nudged by gravity. Had one collision been just a bit more or a bit less energetic, had gravity tugged a little more here or a little less there, the impactor would have had a different size and a different orbit. The dinosaur killer would have struck at some other time in the earth's history, or missed our planet entirely, and dinosaurs would not have become extinct when they did. Who knows, perhaps their 160-million-year reign might have stretched to 225 million years—and they would still be alive today. If 65 million years ago the mammals had found a no vacancy sign, I would not be writing and you would not be read-ing—our species would not exist.
This view of life in the solar system suggests that evolution can be more a matter of chance than inevitability. The dinosaurs did not expire because of a fatal flaw while the flawless mammals lived on. Dinosaurian genes were not inferior to mammalian ones. Life after the K-T event was not an improvement on life before and did not necessarily represent Progress with a capital P. It may be instead that, after the fall, our small, furtive ancestors survived by skulking in burrows and crevices and eating the remains of other creatures, many of whom might have seemed superior to them.
Even the discovery of the Alvarez theory might itself have been due largely to chance. Whether we think it was depends on how we see the work of Jan Smit. The discovery of iridium in the Gubbio boundary clay by the Alvarezes was serendipitous to be sure, but Smit was on the right trail. Had the Alvarezes not gotten there first, would the high iridium levels in his Caravaca samples, hidden in the archives at Delft, ever have come to light, and led him to propose the Smit theory? That we shall never know.
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