| "Rocks are not nouns, but verbs," Marcia Bjornerud writes in her superb new geology book "Timefulness." The ground beneath our feet, the mountains looming overhead, are not static objects, but visible evidence of the processes that shape our planet. The whole story of Earth, from its accretion out of a swirling dust cloud around the sun, through epochs of asteroid bombardments and volcanic explosions and heat and ice and heat again, is inscribed in the layers of rock that have been accumulating like the pages of an unfinished manuscript for 4.6 billion years. Against these impassive witnesses to history, life can seem puny and unimportant. The entire human species has existed for less than 1 percent of the age of the Rocky Mountains. Compared with the billion-year-old marble that makes up the Washington Monument, the whole fraught history of the United States has been little more than a blink of an eye. And yet, Bjornerud writes, life has altered the course of this planet's history. The invention of photosynthesis by ancient microorganisms completely transformed the planet's atmosphere from a methane and carbon dioxide rich haze reminiscent of the exhaust from an SUV, into the oxygen-rich air we now know and love. The colonization of land by plants 400 million years ago slowed the pace at which wind and weather wear down mountains and wash bits of rock into the sea. This shift in global erosion rates transformed the way rivers work, creating waterways that carve deep channels through the Earth that exist today. Though only a dozen minerals existed among the ingredients that formed the solar system 4.6 billion years ago, Earth now boasts more than 4,000 mineral species — almost half of which are the result of biology's interactions with rocks. I find these facts poetic and deeply comforting. Tiny, tenacious microbes, working in concert over a billion years, made our planet a more livable place (for oxygen breathing organisms, anyway). A single stubborn pine clinging to some rocky mountainside helps slow its erosion and shape the course of a mighty river. |
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