Traditional geologic teaching suggests that the continents had converged most recently into the formation of Pangaea approximately 200 million years ago and that at approximately 180 million years ago, a semi-linear rift system developed that split North America from Europe and South America from Africa. What textbooks propose is that a linear source of heat from mantle convection rose along what would become the mid-Atlantic ridge and forced these continents apart and that slow mantle convection caused the Atlantic Ocean to grow as the continents diverged, resulting in the configuration of the continents we observe today. Exactly how this linear heat source (mantle plumes) developed has remained a mystery to geoscientists and the evidence of rifting has never been observed. However, we will digress here to first examine where the idea of Pangaea developed, and why the placement of the continents during Pangaea in the configuration shown in textbooks today is wrong and I’ll explain why.
The idea of continental drift was perhaps first attributed to an Austrian geologist Edward Suess at the end of the 19th century who proposed that the southern continents had been joined into a single continent called Gondwanaland. He assumed that isostatic changes in the crust allowed portions of the continents to sink and create oceans between these continents. Later, in 1912, Alfred Wegner, a German Scientist, noted numerous biologic and geologic similarities along the coasts of Africa and North America. However, he couldn’t postulate how the continents could “plow” through the rocks of the ocean basins to their current locations. He would go on to propose slow drifting due to centrifugal and tidal effects. This, of course was has been found to be incorrect, but his term “continental drift”, although dubbed an impossibility at the time, was later resurrected when new evidences of crustal motion was confirmed. He is also the first to call the supercontinent of conjoined land masses “Pangaea”.
In the early 1960’s Sir Edward Bullard of Cambridge University made several contributions to plate tectonic theory by fitting together the shorelines of Pangaea based on where granitic rocks ended (the true edges of the continental margins) rather than using the present day shorelines. He therefore matched the true continental edges which “fit together almost perfectly” (Bullard 1962, Bullard 1965a). Using seismic marine reflection data along with echo sounder data obtained from the Lamont-Dougherty research vessel Vema, across the Atlantic Ocean to identify a north-south ridge system that formed a similar pattern as the continental boundaries. Bullard’s Pangaea is shown below. Bullard went on to demonstrate that the continents fit together “nicely”. The locations of the continents in Bullard’s Pangaea are still accepted by the scientific community today. However, if we take a close examination of configuration of Bullard’s Pangaea, we can conclude that some serious problems exist.
One huge problem is that most of Mexico and all of Central America are conveniently removed. Where did they go? If one properly connects North America with South America with the proper shape and size of Central America, it would be impossible to obtain the rotation angles shown above. Thus it’s easy to conclude that the shape and angle of the continents have been grossly distorted. In the illustration below, the continents (the actual continental margins) have been placed on a globe instead of a flat map as was done above in order to more accurately show their proper shape and size. Note that there is no feasible way that North America and Africa fit “nicely” when Mexico and Central America are actually included in the map. Furthermore, there’s no way for Europe to “fit nicely” into this configuration either.
Instead, if one aligns the continents to the edge of the mid-ocean ridges instead of along the continental edges, we obtain a much more realistic fit as shown below. This suggests that (1) either the continents were never connected directly, or (2) the crustal material above the mid-ocean ridges has been eroded and removed by some forces not yet addressed. This will be addressed in a future writing.
The purpose of this entry is to get us to see that the continents were never positioned as imagined by Sir Edward Bullard and that this “Pangaea” that is in virtually every introductory geology textbook and accepted as “truth” is simply wrong. Why do we continue to promulgate these false concepts? If the continents were never conjoined as our textbooks point out, then the ancient rifting of the continents that is proposed in our introductory textbooks is also incorrect.
Bullard E. 1962. The Deeper Structure of the Ocean Floor, Proceedings of the Royal Society of London, Series A, Mathematical and Physical Sciences, v. 265, n. 1322, A Discussion on Progress and Needs of Marine Science (Jan. 30th, 1962), p. 386-395.
Bullard E., Everett J.E., and Smith A.G., 1965a. The Fit of the Continents Around the Atlantic, Philosophical Transactions of the Royal Society of London, Series A, Mathematical and Physical Sciences, V. 258, n. 1088, A Symposium on Continental Drift (Oct. 28th, 1965), p. 41-51.