plate tectonic theory Flashcards
What is Plate Tectonic Theory
A scientific theory explaining why the Earth’s crust behaves as it does and how it creates landforms
Who first developed the idea that led to Plate Tectonic Theory
Alfred Wegener, a meteorologist, in the early 20th century
What observation led Wegener to propose his theory
The coastlines of South America and Africa appeared to fit together like puzzle pieces
What did Wegener call the supercontinent that once existed
Pangaea
According to Wegener, how long ago did Pangaea begin to break apart
Around 300 million years ago
What was Wegener’s theory called
Continental Drift
Why was Wegener’s theory not widely accepted at the time
He could not explain how the continents moved
What evidence did Wegener find to support his theory
Fossil evidence linking continents together
What incorrect explanation did Wegener propose for continental movement
He suggested that the Earth’s spin split the continents and dragged them apart
Who proposed an explanation for how continents move in 1929
Arthur Holmes, a British geologist
What was Holmes’ theory
Convection currents in the Earth’s mantle cause continental movement
How do convection currents work
Heated material in the mantle becomes less dense and rises, then cools and sinks again, creating a cycle
What was the early explanation for tectonic plate movement
It was believed to be driven solely by slow-moving convection currents
Why did scientists begin questioning the convection current theory
Plates are too large, and some move in different directions, making it seem unlikely they are only driven by mantle currents
What is gravitational sliding, and why is it important
The idea that gravity plays a major role in moving tectonic plates
What happens to the lithosphere as it moves away from a mid-ocean ridge
It thickens and cools, creating a sloping boundary between the lithosphere and asthenosphere
What is ridge push
Gravity pushes the older part of a tectonic plate away from the mid-ocean ridge due to the weight of thickened lithosphere
What is slab pull
After subduction, the sinking lithosphere pulls the rest of the plate down with it into the mantle
