July 2, 2012 1:00:06 PM
According to a recent poll, almost half of Americans believe that the Earth was created less than 10,000 years ago. Many of them would undoubtedly be proud that they had enough religious faith to believe such a thing, and others just assume it to be true because that's what religious people they trust tell them, along with telling them that scientists are deceiving them in trying to show that the Earth is much older. This embarrassing ignorance is not the reason geologist Doug MacDougall has written Why Geology Matters: Decoding the Past, Anticipating the Future (University of California Press). Indeed, you won't find in his book's index reference to the Bible, creationism, or Bishop Ussher. What you will find in this clearly-written and instructive book is a summary of what geologists do (it isn't just dig for oil or other valuables), how they have come to understand the immense range of times involved in Earth's creation and transformation into our livable world, and most importantly how geology, thought of as the dusty study of ancient ages, is key to understanding the most important of the resource and environmental issues that will confront us in the future. It is a wonderful primer on geology, and a clear explanation of how the science is done.
MacDougall's initial chapter, indeed, tells how the age of our Earth has been pushed back from the folkloric 6,000 years to the current 4.5 billion years. It's a story that has been told before many times, how looking at thicknesses of strata convinced geologists in the nineteenth century that the Earth was very old and how more recently studies of isotopes and overall cosmology have given us our current understanding of how the Earth was formed and when. The rocks from 4.5 billion years ago are no more; geological processes have changed them into other sorts of rock, but that hasn't happened to rocks that have come in from space. Such meteorites can represent the sorts of minerals that were swept up to accumulate in the Earth. The ones containing iron are analogous to the iron core within our planet (and other planets). Then there are meteorites called chondrites which have a texture that indicates they have never melted, and their isotopes show they are unaltered samples of what was floating around when Earth was forming. We have access to the rocks from Earth's outer skin, but chondrites give clues to the Earth's formation and overall composition. Further understanding comes from observation, as from the Hubble telescope, of the intensely powerful processes involved in initiating the formation of stars and planets.
Getting rocks from the Moon, too, has told us much about how it and the Earth formed together. It was originally thought that the Moon was a stray captured by Earth's gravity, but that did not explain why its rocks were so geologically similar to our own. The best explanation now is that Earth had no Moon until a huge collision with another body shortly after the Earth had formed threw out matter from Earth's rocky outer parts. It's why the Moon has low iron content (material from Earth's core was not blasted away) and why the Moon is much less dense than the Earth. The lunar rocks give evidence of how the outer part of the Moon had early in its history been molten, with a magma ocean on the surface. This implies that the same sort of molten surface may have been on the Earth, and this may help explain the complex question of why the Earth's crust (less than 1% of the Earth's volume) is different from the mantle and core below. It is another example of how space science and Earth science work in tandem; there are other examples drawn here from oceanography, biology, chemistry, physics, cosmology, and more. One of the themes in MacDougall's book is that interdisciplinary studies are especially manifest within geology.
Of course there is much here about plate tectonics. It was unimaginable that continents were not fixed but were floating around on the surface of the Earth. Sometimes we simply need science to expand our imaginations. The metallic core of the Earth is gradually cooling, and the heat given off goes to the mantle, fostering slow convection currents which interact with the cold outer lithosphere. This mechanism was poorly understood only fifty years ago, but now makes clear big chunks of geology, like how mountain ranges are formed, why certain regions are prone to earthquakes, and why there are volcanoes in some parts of the Earth and not others. Understanding how big the earthquakes to an area have been in the past is helped by a surprising technique of looking at boulders that are precariously balanced on other boulders. It's still a controversial technique, but an appealing one; if the boulder has sat there without being toppled for thousands of years, then there have been no earthquakes to bother it during that period. It would be nice if the understanding we have gained about tectonics would help us predict earthquakes, but this can seldom be done. There was a prediction of an earthquake around the city of Haicheng in China in 1975, and authorities decided to evacuate the city, which was indeed demolished the next day. This might have been just a lucky break; we can get general ideas of overall earthquake risk, but have little ability to give specific predictions. (Contrary to popular belief, there are no clear links between animal behavior and an impending earthquake. Before the huge 2008 earthquake in Sichuan, China, people saw lots of toads emerging, but it might just have been a sign of spring, not of an earthquake.) Short-term warnings, however, are feasible; such a system is now in place in Japan, where an earthquake will trigger alarms in every school in the country. A few seconds warning could be enough to allow children to take cover.
Chapters here review such topics as atmospheric gases trapped in ice cores from Antarctica, the magnetic polarity stripes in the seafloor, the reasons we believe a meteor wiped out the dinosaurs, the causes of the other four big extinctions, the formation of fossils, and much more. It is a useful and accessible summary, ending with reflections on how studying geology will give us our best chance of handling future problems about water, energy, and mineral resources. Of course MacDougall also shows how understanding geology helps us understand the prospects of global climate change, and he wisely sticks to what we know and what we don't. It does mean something, however, that when carbon dioxide in the air goes up, so do temperatures, and carbon dioxide is now thirty percent higher than at the start of the Industrial Revolution.
We will get further in solving these problems if we know the geology that explains them. We will get nowhere if anti-scientific attitudes are part of the argument when we try to solve scientific problems. When a Christian publication gave a laudatory review of Why Geology Matters, for instance, the influential creationist Ken Ham was shocked, and wrote, "We are seeing more and more articles like this where certain academics who profess to be Christians write about the idea of millions of years as fact. The more Christian writers do this, the more the church becomes indoctrinated with these false ideas that undermine biblical authority (and in reality are examples of bad science anyway)." The processes described MacDougall's admirable summary make no sense at all in an Earth 10,000 years old. Geology, and all the deeply connected sciences mentioned here, don't just tell us accurately how old the Earth is and plenty else about the past. MacDougall presents a convincing case that geology will help us with a better future.