Our Earth has looked radically different in the past compared to today. Supercontinents emerged and broke apart. In their wake, they profoundly changed the course of life, geology, and climate on Earth. They caused sea levels to rise and fall, volcanoes to spew fire, and massive mountains to emerge.
Several continents came together to form a single landmass, creating massive land masses known as supercontinents. The term “supercontinent” refers to the largest land masses that have ever existed on Earth, which have formed and broken up over the course of geological time.
There have been several supercontinents throughout Earth’s history, the most well-known of which are Pangaea and Gondwana. Pangaea was the most recent supercontinent and existed about 335 million years ago, while Gondwana existed about 510 million years ago. These supercontinents formed due to the process of plate tectonics. This idea posits that the crust of the Earth is made up of a bunch of oddly shaped puzzle-like pieces.
When these plates collided and merged, they formed larger land masses, eventually resulting in the formation of a supercontinent. Supercontinents typically break apart after several hundred million years due to the continued movement of the Earth’s tectonic plates.
Before we explore Pannotia, Gondwana, and Pangea, we must first understand the concept of plate tectonics.
In order to understand how supercontinents form and break apart, we must first understand plate tectonics. The scientific community has only recently accepted the concept of plate tectonics. Alfred Wegener prototyped the idea with his idea of ‘continental drift’. Continental drift is the idea that continents float across the ocean floor. Wegener thought this was true because of how South America fits neatly into Africa.
While his idea of the mechanism that moved the continents was wrong, Wegener’s belief that continents move throughout geologic time is absolutely right. Surprisingly, records indicate that map makers from as early as the 1500s suspected that continents had moved over time.
The currently accepted mechanism for the movement of continents is the concept of plate tectonics. The idea that the Earth’s crust is made up of oddly shaped puzzle-like pieces is known as plate tectonics. These puzzle pieces, or tectonic plates, sit on top of the Earth’s mantle, which is the molten center of the Earth. This molten center has currents, sort of like our ocean. These currents of the super-hot, molten mantle move the plates on top of them. These plates collide with one another and separate from one another based on this mantle convection.
A simplified map of Earth’s modern tectonic plates. Red lines indicate plates that are colliding with one another whereas green lines signify plates that are moving away from one another. Map by Hugh Rance via Wikimedia.
Geologists still argue over how many tectonic plates there are. Some people think there are as few as a dozen, while others think there are over 150. The Pacific plate is the largest, which covers about 20% of the Earth underneath the Pacific ocean. The smallest plate may be smaller than the city of Salt Lake City, at 278 square kilometers!
The two main types of tectonic collisions, subduction and uplift, are important to know before delving into supercontinents.
Subduction occurs when two plates move towards each other and one plate slides underneath the other. Typically, an oceanic plate will move below a mostly land, or continental, plate. This is because the thicker continental crust is more buoyant atop the Earth’s mantle compared to the thinner oceanic plate.
Think of it this way. If a huge container cargo ship collided with a small boat, which one would go under the other? The cargo ship would plow overtop the small boat, sending it underwater. The huge force of buoyancy of the cargo ship keeps it floating above the water while the small boat, with its relatively small buoyancy, sinks. The thick continental plates plow over the thin oceanic plates for similar reasons.
As the oceanic plates subduct into the mantle, they form subduction zones. These zones often form coastal mountain ranges, inland volcanic ranges, and earthquakes. The coastal ranges of the western U.S. compared to the volcanic Cascades, which are slightly inland, are an example of this crustal action.
In geology, uplift refers to the vertical movement of the Earth’s crust that results in an increase in elevation or height of the land surface. Tectonic activity, erosion, and sedimentation are among the geologic processes that can cause this.
Tectonic uplift occurs when rocks are pushed up from beneath the Earth’s surface by forces associated with plate tectonics. In areas where two tectonic plates collide, one plate can be thrust up over the other, causing this to occur. Uplifting of rocks can expose them to erosion, which can further shape the landscape.
When weathering, erosion, and other physical processes wear away the Earth’s surface, erosional uplift occurs. This can result in the exposure of previously buried rocks and the creation of new landforms, such as mountains and canyons.
Sedimentary uplift occurs when sedimentary rocks are deposited on top of existing rocks, adding weight and causing the underlying rocks to be pushed upward. This can result in the formation of features such as anticlines and domes.
Uplift can have significant impacts on the environment and human societies. It can create new habitats for plants and animals, provide access to valuable mineral resources, and create new landscapes for human settlement and recreation. However, it can also lead to the formation of natural hazards such as landslides and rockfalls.
The three most recent supercontinents were Pangea, Gondwana, and Pannotia. Geologists think there were other supercontinents before these three. We call them Nuna (or Columbia), Rodinia, and Ur.
One definition of a supercontinent is a single landmass that contains at least 75% of all land on Earth. By comparison, the current African-Eurasian landmass contains about 57% of the land on our planet.
The supercontinent cycle, first proposed by Damien Nance in the 1980s, is a cycle no one organism will ever be able to experience. This cycle happens over the course of hundreds of millions of years. Beginning with a supercontinent, the tectonic plates will eventually begin to drift apart. This drift causes the supercontinent to break up into smaller continents. Eventually the landmasses begin to connect on some other side of the Earth to create a new supercontinent.
We are currently in the part of the cycle between supercontinents. The most recent supercontinent was Pangea, which began to break up about 175 million years ago. This cycle doesn’t happen on regular time intervals. Instead, it is rather random. Surprisingly, the supercontinent cycle has incredibly important implications for the Earth’s climate, biodiversity, sea levels, and general geography (more on these later).
A short-lived supercontinent, centered around the south pole, was Pannotia. Modern-day Africa was at the center of Pannotia. Apparently, the scientific jury is still out on whether Pannotia actually existed. Pannotia existed during the very end of the Neoproterozoic period. Life during this period was pretty basic. Shelled organisms didn’t exist but some kinds of worms did. We don’t have too many fossils from this period and prior to it.
The climate on Pannotia was likely pretty hostile. After the breakup of Rodinia (the supercontinent before Pannotia), Earth experienced a massive glaciation that caused a mass exctinction. The tectonic activity that eventually led to Pannotia also created tons of supervolcanoes that erupted. These eruptions sent cooling sediments and gasses into the atmosphere, causing drastic climate change that supercooled our planet. The icecaps may have covered the entire planet, even in the tropics. This precambrian era couldn’t have been different from the explosion of life that followed.
When Gondwana broke apart from Pannotia, Pannotia ceased to be a supercontinent.
Gondwana was a supercontinent that existed from about 550 to 180 million years ago. It was formed when several smaller continents, including what is now South America, Africa, India, Australia, and Antarctica, collided and merged together.
The name “Gondwana” originates from the Gondwana region of central India. Rocks from the Late Paleozoic and Early Mesozoic eras are exposed there. Scientists believe that these rocks are remnants of the ancient Gondwanan continent.
During the Mesozoic Era, Gondwana was home to a wide variety of plants and animals, including dinosaurs, early mammals, and numerous species of flora. As Gondwana began to break apart, the continents that formed it drifted apart, leading to the formation of the Atlantic, Indian, and Southern Oceans.
Today, scientists find Gondwana remnants spread across the southern hemisphere. Remnants appear across South America, Africa, India, Australia, and Antarctica. The shared geologic history, plant and animal life, and cultural connections between these regions still reflect the legacy of Gondwana.
Gondwana was something of a miniature supercontinent. It didn’t contain all land on Earth, or even close to it, really. Nearly of Earth’s modern southern hemisphere landmasses were part of Gondwana. In addition, the Arabian peninsula, North Africa, and the Indian subcontinent were part of Gondwana. Since Gondwana didn’t approach 75% of Earth’s landmass, some geologists don’t consider it a supercontinent.
The assembly of Gondwana coincided with the Cambrian explosion. Life before the Cambrian explosion was primarily composed of single-celled or simple, multicellular organisms. Geologists begin to see all major animal groups emerge during the Cambrian explosion.
Gondwana’s assembly created the first massive mountain range on Earth. Researchers find remnants of this mountain range in Brazil and northern Africa. These mountains were thought to be Himalayan in scale. The erosion of these colossal mountains sent essential nutrients and sediments into the sea. Scientists think that these very sediments provided the conditions necessary for the Cambrian explosion.
Pangea (sometimes spelled pangaea) was Earth’s most recent supercontinent. This supercontinent contained nearly all the land on Earth. This fact is reflected in Pangea’s name which means ‘all lands’ in Greek. In total, the single continent of Pangea took up about 1/3 of Earth’s surface. The other two-thirds of the Earth was a single ocean, named Panthalassa.
Pangea began forming with the creation of Laurussia. This large continent was created when Laurentia, the core of modern North America, collided with two other continents, Avalonia and Baltica. This collision and uplift created the northern Appalachian mountains. Researchers named this new continent Euramerica. Eventually, Euramerica impacted the northwestern part of Gondwana, which created the southern Appalachian mountains. While they aren’t incredibly tall today, the Appalachians may have been as tall as the modern Himalayas back during the formation of Pangea.
In Pangea, modern Africa and South America were snuggled up against each other. North America butted in with Florida between South America and Africa. Eurasia was connected to the northern part of Africa. When modern borders are superimposed on the Pangean continent, our world doesn’t look too different.
However, life on Pangea did look much different than it does today.
Pangea formed during the two final periods of the late Paleozoic era, the Carboniferous period and the permian period. Life created the amniotic egg during the Carboniferous. Amniotic is just a fancy way to say an egg with a hard shell. Until this time, eggs needed outside moisture to keep them from drying out (think fish eggs). The amniotic egg allowed animals, such as birds and reptiles, to lay eggs in drier areas. As the interior of Pangea dried out, this amniotic egg was crucial to the success of the dinosaurs.
The Paleozoic era ended about 250 million years ago with the largest mass extinction on Earth. This extinction killed about 96% of species. Yikes!
Dinosaurs emerged on Pangea about 250 million years ago during the Triassic period after that nasty extinction. They reigned through the breakup of the supercontinent until the mass extinction about 66 milllion years ago. Apparently, reptiles and dinosaurs liked to inhabit the drier parts of Pangea that had one rainy season. Mammals, on the other hand, lived in wetter places with two wet seasons. During this era, Earth was 38F( (20C) hotter than today! There was 5 to 20 times as much carbon dioxide in the atmosphere, which created a massive greenhouse effect. That extra heat was crucial for the huge, cold-blooded dinosaurs.
The Late Gondwana refers to the period of time in the geological history of the supercontinent of Gondwana that began roughly 120 million years ago and ended with the breakup of the supercontinent into its modern-day constituent landmasses. As this movement occurred, Pangea ceased to exist.
During the Late Gondwana, the supercontinent was dominated by a tropical climate, and a wide variety of flora and fauna flourished. This period saw the diversification of flowering plants and the emergence of new types of dinosaurs, including the theropod and sauropod dinosaurs.
Significant tectonic activity also characterized the Late Gondwana. This included the continued separation of South America from Africa, the fragmentation of India from Antarctica, and the opening of the South Atlantic Ocean.
Today, the remnants of the Late Gondwana can be found in the southern hemisphere, including the African, South American, Australian, and Antarctic continents. A shared geologic history characterizes these regions. They also share a unique plant and animal life that evolved in isolation following the breakup of Gondwana.
Paleogeography, or the study of ancient geography, is the Earth science that studies topics like supercontinents. While I won’t claim to understand their techniques, there are a few easy-to-understand ways they can prove past supercontinents.
First, the geologic record shows that the same types of igneous, basalt, or sedimentary rocks appear in places far from one another. The age of these rocks date back to the formation of their respective supercontinents. For example, the rocks that made those first huge Gondwana mountains are found both in Brazil and northern Africa and date to the same period. This is strong evidence that these two landmasses were in cahoots forming that mountain range. Scientists can use the radioactive decay rate of different elements to get fairly precise estimates of the date of rocks hundreds of millions of years old.
Second, geologists find fossils of the same species in places that are now far apart from each other. For example, the fossils of the same species of small, land-based reptiles have been found on Antarctica, India, and South Africa. Since these species couldn’t have traversed the Atlantic or Indian oceans, it serves as more evidence for Gondwana as a previous supercontinent.
One other way to prove the supercontinent’s existence is through paleomagnetism. When rocks form, their magnetic grains point towards Earth’s magnetic pole. By looking at the orientation of these grains and comparing them to the known location of Earth’s magnetic pole at the time, scientists can get an idea of where the rocks were formed. Think of this paleomagnetic study sort of like an ancient compass.
There are currently several theories about the next supercontinent, although the formation and configuration of a future supercontinent is still the subject of scientific debate and speculation. Some of the leading theories are:
1. Novopangaea: This theory proposes that a new supercontinent will form in the distant future, around 250 million years from now. The continued movement of tectonic plates and the closure of the Atlantic Ocean will result in its formation. The resulting supercontinent would bring together the Americas, Africa, and Eurasia, forming a landmass called Novopangaea.
2. Pangea Proxima: This theory suggests that the Atlantic Ocean will continue to widen, while the Pacific Ocean will continue to shrink. Eventually, North and South America will collide with Africa, and Australia will collide with Asia. Pangea Proxima, the resulting supercontinent, centered around the equator. Scientists believe it will form in around 250 million years.
3. Amasia: This theory suggests that the Arctic Ocean will continue to shrink and eventually disappear. A new supercontinent called Amasia will form as the landmasses of North America and Eurasia merge. Amasi will center around the Arctic Ocean.
While these theories are speculative and subject to revision, they provide a framework for understanding the long-term evolution of the Earth’s surface and the forces that shape it.
Featured image by Fama Clamosa via Wikimedia.