Development Of The Theory Flashcards
What was Wegener’s theory unable to explain
How continental movement could have taken place and his ideas gained little ground
When did evidence accumulate to suggest Wegener was right
1940s onwards
What was discovered that proved Wegener’s theory
The mid-atlantic ridge and a similar feature in the Pacific Ocean later
What created the mid-atlantic ridge
Sea floor spreading
What was the evidence for sea-floor spreading
Alternating polarity of the rocks that form the ocean crust
How does sea floor spreading occur
Iron particles in lava erupt on the ocean floor and align with the earth’s magnetic field.
What is palaeomagnetism
When the lava solidifies and records a permanent record of the earths polarity (palaeomagnetism)
How often does the Earth’s polarity reverse
Every 400,00 years or so
What does the alternating polarity of the Earth result in
A series of magnetic stripes with rocks aligned alternately towards the north and south poles
What does the striped pattern suggest
That the ocean crust is slowly spreading away from the polar boundary. The oceanic crust gets older with distance from the mid oceanic ridge.
What does sea floor spreading suggest
That the earth must be getting bigger. As this is not the case, plates must be getting destroyed elsewhere.
What evidence is there that plates are getting destroyed elsewhere
The discovery of huge oceanic trenches where large areas of ocean floor were being pulled downwards
