How Pangaea Became 7 Separate Continents

Wegener called the ancient supercontinent Pangaea, meaning "all lands" in Greek, and he said it was bordered by Panthalassa, the universal sea. He claimed the lands separated 250 million years ago by the process of continental drift, which means the continents just slowly fractured and went their separate ways.

But simply drifting apart seemed too weak of an answer. It didn't seem possible for the continents to just move along the ocean floor. Something stronger had to be at work.

Did something drive a rift through the continents and force them apart? And could another supercontinent emerge? Figuring out how the continents drifted apart took geological society on a magical mystery tour to the ocean floor.

Although scientists agreed with Wegener that there had been a supercontinent, they disliked the reasoning behind continental drift. To really learn what was behind the breakup of Pangaea, they would need to venture all the way to the ocean floor.

From the 1950s to the 1970s, scientists made some important discoveries about the ocean's crust.

Some of the first breakthroughs came in the field of paleomagnetism, as scientists studied the Earth's magnetic fields. The magnetic properties of rocks are classified either as normal, meaning that they have the same polarity as the current magnetic field, or as reversed, meaning that the polarity is opposite the Earth's magnetic field.

This state of polarity becomes locked in when rock is formed. As scientists looked at the patterns of magnetic rock, the layers didn't quite align the way that they were supposed to, suggesting that the magnetized rock and the continents that surrounded it had moved.

What scientists didn't know was why they had moved.

Tectonic Plate Boundaries

The symmetrical striping pattern of the rock provided some more clues, and so did the topography of the ocean's floor. When scientists began mapping the ocean floor, it looked a lot younger than expected.

For something as old as the Earth, scientists expected to see a lot more built-up sediment. They also found oceanic mountain ranges.

Sea Floor Spreading

Paleomagnetic studies revealed that on either side of the mountain ranges, there was a symmetrical magnetic striping. The oceanic map and the magnetic striping were explained in 1962, when a scientist named Harry Hess conceived the idea of seafloor spreading. Seafloor spreading is the process by which magma within the Earth's crust emerges at the mountain ranges and separates the sea floor.

The magma creates a new section of sea floor, which explained why the oceanic crust looked so young: It was continually emerging as a new floor. The newest rock was closest to the mountain range, with older rock located farther away, and each new layer reversed the magnetic polarity, explaining the striping.

When scientists first realized that new ocean floor was regularly emerging, they thought this must mean that the Earth was expanding. But instead, they realized the ocean floor was like a conveyor belt, and that as the new ocean floor emerged, some of the old ocean floor disappeared into oceanic trenches through the process of subduction.

Earthquakes and Volcanic Eruptions

Seismologists were also noticing at about this time that volcanic activity and earthquakes occurred near the spreading ridges and the oceanic trenches. This geological survey evidence suggested that although the continents were moving, the force did not come from the continents themselves, but rather from the ocean's crust.

These moving slabs of earth were dubbed plates, and their movements cause many natural events, including earthquakes, volcanoes and mountain formations. The study of these plate movements came to be known as plate tectonics.

The theory encapsulates both Alfred Wegener's ideas about continental drift and Harry Hess' discoveries about seafloor spreading. Thus, Wegener's ideas about Pangaea were finally explained.

The continents rest on plates made of a layer of the Earth's crust and its mantle, known collectively as the lithosphere. Plates are different sizes, with some plates more than 124 miles (200 km) thick [source: Kious]. Below the lithosphere is a fluid layer of rock called the asthenosphere.

The plates are rigid slabs almost floating along in the asthenosphere, but scientists still aren't sure what causes the plates to move. They know it's somehow related to convection currents in the continental crust, in which hot materials rise upward as cooler materials flow downward, but they haven't figured out the precise relationship.

Scientists do know four different ways the plates move, though.

Now that we know a little bit about how plates move, we can turn again to supercontinents. The planet the oldest supercontinent is known as Rodinia, and it formed about 1 billion years ago [source: Encyclopædia Britannica].

The evidence for all of the supercontinents is limited because the sea floor is always regenerating itself, so Pangaea, the youngest, has the fullest geologic record.

Before Pangaea became a supercontinent, it existed as different continents. Three large continental plates came together to form what's now the Northern Hemisphere, and that landmass merged with what is now the Southern Hemisphere. Pangaea existed during the late Paleozoic and Mesozoic eras, or about 200 million years ago [source: Oreskes].

Pangaea Births All the Continents

Pangaea existed for approximately 100 million years before it began to divide into all the continents we know and love today. First, the continents broke into two large landmasses:

Laurasia split into North America and Eurasia, and Gondwanaland produced Africa, Antarctica, Australia and South America, with some of the pieces rotating slightly as they separated.

As the continents broke away from Pangaea, the Paleo Tethys Ocean formed, eventually growing into what we call the Indian Ocean today. The two continents of North and South America split from Europe and Africa and headed far westward, with the water filling in the gap becoming the Central Atlantic Ocean.

The plates continue to move today, with the most action these days located at the East African Rift. Some geologists think that if they keep moving, the three plates that meet at the African coastline will separate, causing the Indian Ocean to flood the area and separating the Horn of Africa from the mainland [source: Kious]. (In short, Africa is splitting in two.)

How fast does all this happen? The magnetic striping around the places where the sea floor spreads provide a way to measure the continental movement, which, in some places, nears a rate of almost 4 inches (10 centimeters) per year [source: Skinner].

The Mid-Atlantic Ridge moves less than 1 inch (2.5 centimeters) a year, so over millions of years, the South Atlantic Ocean has gone from being a tiny inlet to the size we know it today [source: Kious]. Scientists like to compare the speed at which continents move to the speed at which our fingernails grow [source: Reina].

Although the movements are slow, Africa is moving toward southern Europe, and Australia and south China will collide one day [source: Encyclopædia Britannica]. These are the first movements toward another supercontinent.

Scientists predict the next supercontinent will reconnect in another 250 million years. This process of landmasses coming together and spreading apart is now known as the supercontinent cycle.