[Music] in this lesson we are going to discuss the mechanisms of plate movements at the end of this video lesson you should be able to discuss the mechanism on how tectonic plates move the continental drift theory was not widely accepted because of the belief that continents in ocean basins have always been permanent features on the earth's surface this belief is called permanentism this is what was generally believed about global geology before plate tectonics in spite of the pieces of evidence wegener has mentioned he failed to provide a visible explanation on the driving force or mechanism of his theory what he uses explanation for his theory is the pole fleeing force he believed that pangea originated near the south pole and that the centrifugal force of the planet caused the protocontinent to break apart and result in continents to drift towards the equator this idea was quickly rejected by the scientific community primarily because the apple forces generated by the rotation of the earth were calculated to be insufficient to move continents unluckily he died in 1930 without having an accepted driving force for his theory twenty years later during the cold war both global superpowers the u.s and the soviet union started to study and map the ocean floor they needed this information to plant routes for their nuclear submarines however this becomes a scientific revolution as a result of their study of the ocean floor the submarines gave the first detailed map of the ocean floor which helps scientists understand the geology of the seafloor the geologist and united states navy officer which is tagged as one of the founding fathers of the unifying theory of plate tectonics is harry hess [Music] this figure shows the map of the sea floor protruding or elevated regions of the seafloor are called regis this underwater land formations are the earth's spreading centers ridges are found and formed in mid oceans thus giving the name mid ocean ridges the structure is where new cross prices the new cross then pushes both sides of the ridge thus making the ridges as the spreading centers a famous mid-ocean ridge is the mid-atlantic ridge found in the middle of the atlantic ocean this specific type of fridge is responsible for the separation of the north american and eurasian plates and the south american and the african plains at one end of these spreading centers the old crust may reach a depression called the trench these trenches are the deep parts of the ocean floor which serve as the subduction zones in subduction zones one plate will go underneath the other it is always the denser plate that will sink in the case of an oceanic continental subduction the oceanic plate will go underneath the continental crust because the oceanic crust is denser in the case of a subduction involving two oceanic plates the older or colder plate will go underneath the other because older oceanic plates are denser than younger oceanic plates an example of a popular trench is the mariana trench the reason why it is the deepest point of the ocean is because it is a subduction zone between the pacific plate and the philippine plate this figure summarizes the connection of the mid ocean ridge and trench newly formed oceanic crust will spread out until it gets old and reaches the subduction zones or trenches this means that older ushani crusts are found farther from the mid-ocean ridge harry has called this feature of the ocean floor a seafloor spreading let us now discuss the driving mechanisms of plate movements the first mechanism is a gravity driven mechanism the crust which spreads from the reach travels to the trans or the subduction zone gravity is said to be responsible in pulling the cross from the reach this feature is called slab pool as it reaches the subduction zone it partially melts and rises to the crust above it as magma thus forming volcanoes and volcanic islands since the cross which is abducted is cooler than the rest of the cross on the earth's surface it undergoes heating as it reaches near the asthenosphere as a result of the slab pool the rest of the underlying crust is pushed out of the ridge thus the feature is called reach push this mechanism is analogous to how conveyor belts function this mechanism is not widely accepted because the force of gravity is negligible or too weak to cause the movements of the cross and the landforms and bodies of water above it what is widely accepted is the mantle convection theory magma in the stenosphere is heated near the core which decreases its density thus it would go up to the reach and push the plate riding onto it as the magma is cooled near the surface of the earth it becomes denser thus it will go back down near the core while dragging the plate into the trench the main driving force of these theory is the earth's internal heat from the core the siri also shows the interconnectedness of the layers of the geosphere this driving force can also be explained by looking at the solid state flow model in the earth's core radioactivity causes magma to rise where it expands to produce the plates above earth's surface the older dancer plates descend replacing the hotter material below this is analogous to the water in heating setup as energy is added to the liquid in the form of heat the liquid evaporates or boils thus the water moves from a hotter region to a cooler region the water vapor then condenses as it moves from a colder region to a hot region it is heated again by the heat source and the cycle goes on and on to summarize this lesson let us review the following key points the continental theory was not widely accepted in the early 90s due to the lack of a clear driving mechanism seafloor spreading shows how crust is formed and regis and subducts or gets destroyed in trenches the gravity-driven mechanism involves reach push and slab pool and lastly the mantle convection theory is the currently accepted mechanism of the continental drift because of the energy given by the earth's internal heat and that ends our discussion on the mechanisms of plate movements [Music] you