By Dr. David W. Barber
The remarkable fit between the west coasts of Africa and Europe and the east coasts of North and South America has long puzzled cartographers who began putting together maps of the world during the rapid exploration and development of trade routes across the oceans. First noticed by the Dutch cartographer Abraham Ortelius in 1596 as he was creating the first modern atlas, this observation led many other scientists to investigate the possibility that continents were not stationary but had migrated across the surface of the earth through time. However, most geologists opposed this notion because rocks were solid, at least on the surface. How could the solid rock of the continents push through the solid rock of the ocean floors? No mechanism for such a process seemed to exist.
The apparent fit of the continents did not disappear so other observations were added to the evidence that supported the idea that the continents seemed to be mobile. Advanced technology such as using borehole logging software helps support this evidence. The distribution of ancient fossils, rocks and mountain ranges, and the locations of ancient climate zones seemed to point to a time when the continents were fused together in one super continent. Despite the mounting amount of evidence that would support such a conclusion and a growing number of scientists that contributed to that evidence, the lack of any known mechanism for producing such a phenomenon kept this idea from gaining a foothold in conventional scientific wisdom.
German meteorologist Alfred Wegener gave this theory its name, continental displacement (drift), and called this supercontinent Pangaea in a lecture to Frankfurt’s Geological Society in 1912, causing little reaction. Not until his book, The Origin of Continents and Oceans, originally published in German in 1915, was published in English in 1922, did the shouting start. The mechanism for the motion he proposed was the spin of the earth, but most geologists rejected such a mechanism as being too weak to move the mass of a continent around. Also, Wegener was not a geologist but a meteorologist, so his expertise in such matters was questionable.
The resistance to his theory was particularly fervent in the United States, and American geologists were very hesitant to investigate the truth of his arguments for fear of losing credibility among their peers. When Marie Tharp showed the results of the seafloor mapping of the mid-Atlantic ridge to her boss, Bruce Heezen, in the early 1950’s, he initially totally rejected her observations because they looked like continental drift, an anathema for a career in geology at that time. Not until corroborating evidence from earthquake loci in the Atlantic overlaid the ridge topography perfectly did he accept and publish the results in 1957. The exact mechanism for such a process still remains a mystery, but the current theory of plate tectonics has now become the prevalent paradigm for measuring and predicting large scale motions and behaviors of the continents and the ocean plates.
What is a paradigm and, specifically, what is a scientific paradigm? Broadly speaking, a paradigm is a model or pattern that helps guide and develop our thinking and how we investigate and understand a process we are studying. The scientific method is a good example of a paradigm that has governed the empirical method of acquiring scientific knowledge since at least the 17th century. Starting from careful observations that describe a problem, this method instructs us to create a hypothesis that explains the problem, test the hypothesis, and then draw conclusions and refine the hypothesis. This methodology has produced great advances in our understanding and manipulation of the physical world around us over the last 400 years. The crux of the method is the creation of the hypothesis; until you establish the correct hypothesis, the results of your tests will remain inconclusive, no matter how close you come to “proving” the correlation. At best, the results of the scientific method are inferences, or conclusions that are reached based on evidence and reasoning.
Geological systems generally involve a variety of processes both large- and small-scale, are multi-disciplined in nature, and include data sets that range from precise measurements to rough approximations. The long-term nature of geologic time over which these processes operate further complicates their study, and the remote location of many of the fundamental processes limits the ability to study them directly. Therefore, geology offers unique challenges to the geologists who study the processes which affect the long-term behavior of the earth. The placement of the continents throughout the history of the planet is just one of many questions that confront geologists.
The evidence for the mobility of the continents has only increased since the 1960’s, and the theory of plate tectonics has provided a more inclusive model, or paradigm, than continental drift to explain the apparent movement of continental masses through time. The recognition that the crust of the earth is composed of separate plates of rock that can float around the surface on top of a more viscous mantle provided a mechanism for their apparent drift through time. Not that the processes involved are completely understood, but at least there is a way now for solid rock masses to separate from each other slowly but surely just as the evidence for continental drift inferred.
The theory of continental drift, as a paradigm, actually has been confirmed; the continents are moving. Plate tectonics has replaced it only by providing a more complete mechanism for allowing the continents to be displaced. As a paradigm, plate tectonics provides more evidence and additional areas of study to fully understand the mobility of the continents. But it is still in the lineage of its father, the patriarch of mobility, continental drift.
