How quickly time flies. It was one hundred years ago today that Alfred Wegener introduced the concept of continental drift to modern science. His hypothesis remained controversial for decades, in spite of evidence ranging from the matching contours of coastlines separated by oceans (think about how nicely eastern South America and western Africa fit together), to similar plant and animal fossils found on opposing shores, to the matching distribution of glacial sediments across continents. Wegener had discerned the phenomenon, but he did not have the resources to explain the mechanism. That came along half a century later, when the theory of plate tectonics was fully developed ~ the earth's surface (including the sea floor) is a crust comprised of a network of plates in constant motion, riding on circulating currents of molten magma beneath. Plates are generated along mid-oceanic ridges where upwelling magma spreads in both directions from the ridge (seafloor spreading). When one plate collides with another, it may compress and push the second plate upward, forming our youngest and highest mountain ranges (the Himalayas, the Andes, the Rockies). Or, one plate may simply be forced beneath the other, to re-enter the molten substrate. Or, the sides of the two plates may simply bear against each other while moving in opposite directions. All of this activity is responsible for the bulk of the earthquakes and volcanoes which occur along plate boundaries. The image above (click to enlarge) illustrates the processes, and the image below shows the shapes and distribution of the global network of tectonic plates.
Wegener's story is similar to that of Charles Darwin, who proposed the theory of evolution through natural selection, but did not possess the resources to grasp selection's driving mechanism ~ genetics. It wasn't until Gregor Mendel published the results of his study of genetic inheritance among pea plants that the narrative was filled in. Still, both Wegener and Darwin were the visionaries whose minds were able to look at the concrete world and deduce explanations for what they saw.
And now, with a trumpet fanfare and a flourish of tympani, here are the most popular Scientific American blog posts of 2011. Inclusion in this list of 30 essays is a high achievement among science writers, and I'm pleased that several of my Google+ friends made the list ~ Christie Wilcox (# 8 and 10), Jennifer Ouellette (# 12), and Andrea Kuszewski (# 1). Each title on the list links to the corresponding essay, so that you can get a taste of the rigor, insight, originality and quality which these writers have in common.
As a bonus, here is a link to Jennifer Ouellette's appearance on the Craig Ferguson show. Pretty hilarious.