2.1.5 The Lithosphere (KQ1): Evidence of Plate Tectonics

How do we know that the plates have moved...where's the evidence?  We know that earthquakes and volcanoes happen, we know that there are mountain ranges and deep and shallow parts of the ocean...but how do we know it's caused by plate tectonic movement?

This teacher does a really great job of explaining it in terms of paelo-magnetism (see below)...so instead of reinventing the wheel, let's watch him and learn.

KEY POINTS TO TAKE HOME: 

• The continents seem to "fit" together...this is known as geologic fit
• We know from looking at layers of rock that the magnetic poles on Earth switch every so often (by every so often, I mean hundreds of millions of years)
• The magnetic rocks on the crust change poles as you move away from known ridges
• On both sides of the ridge, the distance is the same to change the pole, showing that the rock equidistant from the ridge on both sides was formed at the same time
• The is evidence that the plates are moving away from each other
• This theory and the evidence is known as paleo-magnetism

One more piece of evidence (my favorite) is from what a lot of kids want to be when they grow up when they're in elementary school...dinosaur bone diggers (paleontologists)!  There have been bones of pre-historic creatures (namely the mesosaurus) and plants found on and near South America and South Africa, suggesting strongly that at one point they were connected...there is no other reasonable explanation for finding two of the exact same species that far apart.  This evidence is basically known as paleontology...or fossil evidence.