In recent issues, The PEGG has invited readers, in a maximum of 200 words, to share what they consider to be an important technical or professional development of the 20th century. Our first submission comes from L. Mark Larsen, P.Eng., P.Geol., of Calgary, who writes:

A great scientific idea of the 20th century was the development of the theory of plate tectonics. The very idea of mobile continents floating and moving, sometimes colliding and welding together, sometimes rupturing and splitting apart, throughout earth's history, appeared preposterously absurd to educated peoples a century ago.

Yet, even a casual observer will note the coastlines of eastern South America and West Africa fit together like pieces in a jigsaw puzzle. Alfred Wegener citing similarities in the rocks, fossil plants and animals, climatic and glacial patterns, suggested the two continents had been together in late Paleozoic time and subsequently drifted apart.

The hypothesis was hotly debated during the 1920s and 1930s but was rejected by most earth scientists for the lack of a suitable mechanism. Subsequent mapping of the ocean floor and paleomagnetic studies ultimately allowed reconstructions supporting the model of a dynamic earth with convection currents in the earth's mantle as the mechanism for movement.

Accumulated evidence has transformed the former crackpot hypothesis into a well-accepted model of the earth. This started a revolution in geological thought, adding insight to virtually all branches of the geological sciences, from pure research topics to mineral and petroleum exploration.