This morning I came across a remarkable website that attempts to illustrate the concept of deep time using a metaphorical 12 hour clock. As I stated before in The Ratchet, metaphors like this are necessary for the human mind to conceptualize millions and billions of years. They are also necessary to conceptualize some biological events like speciation and most geophysical events like the formation and separation of continents. This is because phenomena like speciation and the separation of continents occur on larger time scales than we are accustomed to experiencing.
In fact, the process of plate tectonics (which causes the formation and separation of continents) occurs so slowly that our collective popular imagination has really only allowed for the incorporation of one supercontinent: Pangaea. Most people have heard of Pangaea from high school geography class (or from the animated film Ice Age: Continental Drift, which incorrectly includes the separation of the supercontinent within its narrative). However, few people are aware that Pangaea is not the first supercontinent to have existed on Earth, nor will it be the last.
Pangaea existed between 300-200 million years ago during the late Paleozoic and the early Mesozoic. During this time the clade Dinosauria evolved and dominated the terrestrial landscape.
But the Earth is 4.5 billion years old and geologists have realized that our planet goes through supercontinent cycles that occur roughly every 600 million years. This means that Pangaea was not the first supercontinent; it was just the most recent supercontinent, which makes it the easiest to conceptualize.
During the first billion years of Earth’s existence continents as we know them today probably did not exist. Once the Earth cooled oceans dominated the surface. However, proto-continents began to form driven by the slow movement of Earth’s super hot semi-solid mantle. Geologists are still unsure if supercontinents existed during this period of our planet’s history. Some suspect that parts of modern day Madagascar, India, and Australia were connected but this claim is still highly controversial and not known with a high degree of certainty. But even if a connected landmass did exist at this time, it would have only been half the size of modern day Australia!
The Three Known Giants
Columbia - 1.8 billion years ago
Evidence of the Earth’s terrestrial composition is far more reliable as we approach what many geologists consider to be the “first true supercontinent”: [Columbia](http://en.wikipedia.org/wiki/Columbia_(supercontinent). Columbia existed 1.8 billion years ago in the Paleoproterozoic Era. Although this landmass was 50 million square kilometers in size, that is quite small when compared to the 150 million square kilometers of land exposed on Earth today. For some further context Afro-Eurasia alone is 84 million square kilometers, almost double Columbia’s size. However, after approximately 200 million years Columbia split leading to a new era of continental drift.
Rodinia - 1.0 billion years ago
Rodinia was the next supercontinent to form approximately 1 billion years ago in the Neoproterozoic era. Although it was larger than Columbia, Rodinia formed entirely south of the equator. Like Columbia, Rodinia was completely devoid of life. The supercontinent existed before the Cambrian Explosion and all life (both single-celled and multi-celled) had yet to transition to a terrestrial niche. When Rodinia began to separate (~750-650 mya) it may have initiated a transformative global environmental period: Snowball Earth.
Our beloved Pangaea was the next in the succession of supercontinents. It was the first supercontinent to possess life and was home to the first major proliferation of megafauna on our planet. Pangaea may have allowed dinosaurs to become globally dominant quickly because there were no major oceans separating populations. Many paleontologists believe that Pangaea also contributed to low genetic diversity within the Dinosauria clade and a homogenization of general dinosaur body plans. The most obvious physical evidence of Pangaea’s existence can be noticed an any world map: the South American and African coasts (which appear to fit like two pieces of a jigsaw puzzle).
Today many geologists believe we are in a half-way point between supercontinental cycles. We know that a future supercontinent will exist, but we are unsure of what type of supercontinent it will be. Currently there are three different models: Pangaea Ultima, Amasia, and Novopangaea. These three forms are all based on calculations of contemporary incremental movement and fragmentary data of plate tectonic dynamics.
In the Pangaea Ultima scenario the Atlantic Ocean will start to close, opening up the Pacific once again. North American and Africa would collide, South American and Antarctica would collide, and Australia and South-East Asia would collide.
In the Amasia and Novopangaea scenarios the Atlantic Ocean would become the “super ocean” and the Pacific would close. In these scenarios the Americas would crash into Asia, but it is unknown whether Antarctica would join the other continents in the Northern Hemisphere.
Either way, current calculations predict this future supercontinent will exist in 250 million years.
The study of plate tectonics is remarkably young and geologists have just started to figure out our planet’s continental history (and potential future). The effects that major continental collisions and separations have on ecosystems are profound. Future research should reveal more about how they affect climate and biodiversity. But in my opinion we already have enough data to reveal the astounding fact that if you were to go backwards or forwards in time 250 million years, our planet would look like an alien.
Like life itself, our planet is undergoing constant change. This means that the number of future supercontinents will only be limited by the life of our star.
(Below is a video illustrating the past 250 million years of continental drift and the next 250 million years of continental drift under the Pangaea Ultima scenario):