Evolution of Evolution — Text-only | Flash Special Report
Charles Darwin’s Impact on Geology
Evolutionary ideas have both direct and indirect effects on geosciences
By Judith Totman Parrish
One of Darwin’s contemporaries, Charles Lyell, published “Principles of Geology,” the first book to discuss the Earth as we do today. Lyell described Earth as a series of gradual processes, not solely the catastrophes envisioned by previous workers. He established important ideas about earthquakes and volcanoes, and his picture of Earth history as a grand procession of change would greatly influence the thinking of one of the world’s foremost naturalists, Charles Darwin.
“Principles of Geology” appeared just before Darwin’s voyage on the Royal Navy ship HMS Beagle, prompting him to make careful observations of geological events including earthquakes and volcanoes during his journey. Darwin’s most direct geological contribution was his explanation of the origin of atolls, the annular coral islands that dot the western Pacific Ocean. He observed many different kinds of islands and realized each represented a developmental sequence—from the earliest stages as reef-ringed, extinct volcanic peaks, to the latest stages of barely submerged coral reefs with central lagoons. Although Darwin was only partially correct when he attributed the evolution of the islands to reef growth and erosion, his explanation played an important role in future understanding of seafloor spreading and the now widely accepted theory of plate tectonics, which describes the large-scale movement of the Earth’s outermost shell.
Most people think of evolution as relating to biology and paleontology. What they don't realize is that most paleontologists are also geologists, who use fossils to date rocks and study past environments. Darwin’s Theory of Evolution is the structure that supports these efforts.
Biostratigraphy is the science of dating rocks by the fossils they contain, and it was just getting started in Darwin’s time. Scientists noticed that certain types of fossils appear in the same sequences everywhere in the geologic record. They reasoned this was because certain organisms lived only at specific times. This meant the sequence of fossils could be used to date rocks relative to each other and to correlate the age of rocks from place to place. It was application of a Darwinian idea—that the sequence of fossils through time represents successive events of evolutionary change and extinction—that put the geologic science of biostratigraphy on a much stronger footing. Later, this relative time scale of fossil sequences would be calibrated with radiometric dates.
Other geologic sciences also use Darwinian principles. For example, taphonomy and paleoecology rely on understanding evolution and natural selection to determine past environmental conditions. Taphonomy looks at how organisms decay and become fossilized over time, and paleoecology uses fossils to reconstruct information about past ecosystems.
Much of what we know about past climates, including the temperature record, humidity, rainfall and other factors, comes from our understanding of fossils. Evolution and natural selection allow us to interpret changes in the form and species of plants as the climate changed. We rely on this knowledge to understand how plants respond to climate and how that response might be recorded in the fossil record. Because the Theory of Evolution helps us understand fossils in their environments, geologists’ interpretations of the rocks are far richer and more nuanced than they could be without it.
Darwin’s theory revolutionized and became the foundation for all of biology, but for the reasons mentioned above, it was just as much the foundation for geology as well. The inexorable changes that Lyell wrote of were echoed by Darwin in the Theory of Evolution and, in turn, echoed back to geologists in a coherent sense of how Earth—and the life upon it—changed; when those changes occurred; and, how what we see today, is a product of that long history.
Judith Totman Parrish is professor of geological sciences at the University of Idaho. Her education includes a BS and MA in Biological Sciences and an MS and Ph.D. in Earth Sciences, all from the University of California, Santa Cruz; followed by a postdoctorate at the University of Chicago. Her field is pre-Quaternary Era paleoclimatology. She is currently (2008-2009) president of the Geological Society of America. The National Science Foundation supports her work on the evolution of the Pangean Megamonsoon: Plant Taphonomy in Triassic Sedimentary Rocks of the Ischigualasto Basin.
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