Around 500 million years ago, the super continent Pangaea had yet to form. At that time, geologists believe that what is now the North American shoreline ended near the eastern New York border and almost none of the land that today define as New England was attached to North America. Instead, the land masses of Deerfield and surrounding New England were big islands on the earths crust called exotic terraces. During the collision between the African, European and North American continents these terrace were smashed between North America and Western Africa, forming Pangaea (image top right).
In terms of how we know what we know, Raymo tells interesting stories revealing that when the first reasonably accurate maps of the Atlantic Ocean were drawn in late sixteenth century, people noted that the two sides of ocean continents matched like jigsaw puzzle pieces. Largely from the observing similar rock formations along the eastern coast of South America and the western coast of Africa, the German meteorologist Alfred Wegener proposed in 1915 that all the continents were once united in a supercontinent, Pangaea. Wagener proposed that Pangaea broke apart with continental drift accounting for the present positions. His theories were examined, then rejected by prominent geologists of the time. It was not until much after his death in the 1960s when continental drift and the theory of Pangaea was revived.
Raymo continues the story recounting that the technology of echo sounding (sonar) made possible the mapping of the sea floor that revealed a system of ridges on the ocean basins. Apparently, if it were possible to drain all the water from the oceans, as when emptying a bathtub, the undersea mountain ranges would be the most dramatic of all global ranges. In the Atlantic, the ridge lies exactly in the middle of the ocean basin and at this ridge there is an outflow of heat from the earths interior. The outflow of heat yields seafloor rocks that are youngest at the ridge and oldest near the continental margins. American geologist Harry Hess in 1962 took these observations and developed the theory of sea-floor spreading. Hess maintained that the entire earth crust is cycled through the earth’s interior every several hundred million years. This great looping motion of matter is driven by heat convection in the Earths interior – by the tendency of hotter matter to rise and cooler matter to sink in these great convective loops (image upper left).
As the continents collided forming Pangaea, subduction occurred where one place slid underneath another and forced bedrock upwards, generating the Appalachian Mountains. These mountains, once the size of the great Himalayan ranges today, folded and deformed the deep bedrock into metamorphic rock types gneiss, schist, slate and marble. As these continental collisions and folding bedrock occurred, other subterranean zones that had melted cooled slowly, crystallizing into granite that underlies the Deerfield Basin.
For perspective on these geological events it’s worth considering geological time put into a geological clock (below). Earth began at 12:oo, life at 2:00, photosynthesis at 3:00, oxygen rich atmosphere at 6:00, eukaryotes at 6:30, cambrian explosion at 10:00, Pangaea forming at 11:00, with the arrival of dinosaurs shortly to follow.
