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How Continents Move
Look at a map of the world. The eastern coast of South America seems as though it could fit next to western Africa like pieces of a puzzle. When the same types of fossils were found on both continents, scientists began to think that they might have been attached in the geological past. In 1915, Alfred Wegener proposed that the surface of the Earth changes through time and that the position of continents we see today looked very different over time. The scientific community rejected Wegener’s theory of “Continental Drift” because there was no explanation of how the continents moved.
In the 1960s geologists discovered that active geologic features such as volcanoes and earthquakes occurred along distinct belts around the world. We now recognize these belts define the edges of the tectonic plates that make up the Earth’s crust.
In the 1960s geologists discovered that active geologic features such as volcanoes and earthquakes occurred along distinct belts around the world that define the edges of the tectonic plates that make up the Earth’s crust.
The crust of the Earth is thin compared to the size of the planet, only about 6 to 35 kilometres thick. It is almost 6300 kilometres to the centre of Earth. Heat generated within the planet creates convection currents bringing new material to the surface where it cools to create new crust. Molten material erupts along volcanic mountain chains where it spreads out to create the ocean floor. As the crust ages and cools it eventually sinks back into the mantle to be re-melted. The denser crust sinks while lighter crust melts and slowly bubbles back toward to the surface. Over billions of years the lighter material that has risen to the surface has formed the continents that are pushed about as new oceans are created and destroyed.
The crust of the Earth is thin compared to the size of the planet, only about 6 to 35 kilometres thick. It is almost 6300 kilometres to the centre of Earth. The crust is 6 to 35 km; the mantle is 2900 km; the outer core is 2000 km; and the inner core is 1370 km. Convection currents bring molten material to the surface where it cools to create new crust. Lava from the mantle erupts along volcanic mountain chains where it spreads out to create the ocean floor, for example along the Continental Crust and the Oceanic Crust creating the mid-Oceanic ridge.
The concept of seafloor spreading provided the final answer to the question of how continents move. Paleomagnetic data from the Atlantic Ocean showed that the ocean floor was spreading outward from a Mid-Atlantic Ridge of volcanoes. New ocean floor erupted at the ridge and older ocean floor was pushed outward. We see this process in Iceland comprised of volcanic islands on the Mid-Atlantic Ridge.
When plates move apart to form new crust in one area, plates must converge or come together in another area where crust is destroyed. An example of this is seen where the modern Pacific Ocean is subducted beneath the Asian continent. The destruction of the crust in a deep ocean trench results in the earthquakes and volcanoes in places like Japan and Indonesia.
The core of Earth is hot and causes convection currents in the mantle. Hot material rises, sometimes breaking through to the surface as volcanoes. Molten material breaking through the surface creates rift valleys that split the continents. As the crack widens new oceans are created by sea-floor spreading. Molten rock cools as crust and separates into light and heavy rock types. Lighter rocks at the surface form continental crust and heavier rocks are subducted back into the mantle to be re-melted and go through the cycle again.
The movement of the Earth’s crust through plate tectonics has caused dramatic changes to the way continents are shaped and where they are located. At times in Earth history continental crust has come together to form supercontinents, only to break apart again. New Brunswick’s past goes back a billion years to a supercontinent called Rodinia. This supercontinent broke apart about 700 million years ago, its fragments scattered across the globe. The most recent supercontinent called Pangea brought the continents together about again 250 million years ago. Since then, the continents have split apart again to form our modern world.
