Plate Tectonics: New Findings Fill Out The 50-Year-Old Theory That Explains Earth’s Landmasses

Satellite image of California’s San Andreas fault, where two continental plates come together. NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team, CC BY

Fifty years ago, there was a seismic shift away from the longstanding belief that Earth’s continents were permanently stationary.

In 1966, J. Tuzo Wilson published Did the Atlantic Close and then Re-Open? in the journal Nature. The Canadian author introduced to the mainstream the idea that continents and oceans are in continuous motion over our planet’s surface. Known as plate tectonics, the theory describes the large-scale motion of the outer layer of the Earth. It explains tectonic activity (things like earthquakes and the building of mountain ranges) at the edges of continental landmasses (for instance, the San Andreas Fault in California and the Andes in South America).

At 50 years old, with a surge of interest in where the surface of our planet has been and where it’s going, scientists are reassessing what plate tectonics does a good job of explaining – and puzzling over where new findings might fit in.

Evidence for the theory

Although the widespread acceptance of the theory of plate tectonics is younger than Barack Obama, German scientist Alfred Wegener first advanced the hypothesis back in 1912.

He noted that the Earth’s current landmasses could fit together like a jigsaw puzzle. After analyzing fossil records that showed similar species once lived in now geographically remote locations, meteorologist Wegener proposed that the continents had once been fused. But without a mechanism to explain how the continents could actually “drift,” most geologists dismissed his ideas. His “amateur” status, combined with anti-German sentiment in the period after World War I, meant his hypothesis was deemed speculative at best.

In 1966, Tuzo Wilson built on earlier ideas to provide a missing link: the Atlantic ocean had opened and closed at least once before. By studying rock types, he found that parts of New England and Canada were of European origin, and that parts of Norway and Scotland were American. From this evidence, Wilson showed that the Atlantic Ocean had opened, closed and re-opened again, taking parts of its neighboring landmasses with it.

And there it was: proof our planet’s continents were not stationary.

The Conversation

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The 15 major plates on our planet’s surface. USGS

How plate tectonics works

Earth’s crust and top part of the mantle (the next layer in toward the core of our planet) run about 150 km deep. Together, they’re called the lithosphere and make up the “plates” in plate tectonics. We now know there are 15 major plates that cover the planet’s surface, moving at around the speed at which our fingernails grow.

Based on radiometric dating of rocks, we know that no ocean is more than 200 million years old, though our continents are much older. The oceans' opening and closing process – called the Wilson cycle – explains how the Earth’s surface evolves.

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