Notes

In the year 1912, geologist Alfred Wegener observed these similarities among the continents and hypothesized that they all must have been part of a single giant continent. Additionally, he said that massive supercontinent was surrounded by one enormous ocean that covered the remainder of the planet. Wegener believed this supercontinent, which he called Pangaea, somehow broke apart into separate continents. Eventually, he proposed, those continents drifted into the locations where they are today.


Alfred Wegener, developed the Theory of Continental Drift
Scientists who study fossil records and other evidence of prehistoric life to determine its interactions with its environment are called paleontologists. About the same time that Alfred Wegener began developing his Theory of Continental Drift, paleontologists claimed to have evidence that could have supported the idea. Specifically, fossils from the west coast of Africa were compared to fossils from the east coast of South America. If you look closely at the image of the world again, you'll see that these two coasts line up pretty closely. Fossil evidence indicated that similar species of wildlife inhabited both continents.
Visually, Wegener's theory made sense. However, even with strong fossil evidence, scientists at the time failed to see how such a cataclysmic change could have occurred with land masses so large. In other words, Wegener's reasoning for continental drift was nothing more than coincidence if he couldn't explain what forces could have caused such massive pieces of land to break and drift so far apart.
After Wegener died, a scientist named Arthur Holmes hypothesized that perhaps the continents moved apart as the result of a process called thermal convection. This is the idea that heat circulates upward from the lower mantle into the upper mantle and crust, the two layers that make up the Earth's land masses. Holmes believed the harder crust and upper mantle rested atop a hot, flexible lower mantle. Despite the fact that Holmes' hypothesis bore factual truths, at the time scientists had no way of proving it. Many years later, in the 1960s scientists were finally able to corroborate Wegener's and Holmes' theories with geological evidence.
Representation of what Pangaea may have looked like as the continents broke apart and eventually drifted to where they are now.
Today, scientists firmly believe Earth's continents once formed a massive supercontinent named Pangaea. Plate tectonics is also universally accepted as an explanation for continental drift, which still occurs today. The level of extreme force necessary to move continent-sized land masses is incredible. Throughout the remainder of this unit, we'll take a closer look at plate tectonics and the geothermal activity that contributes to this process.