The continental plates are more or less loose from the oceanic plates which are heavier and of other material (basalt) and because continental plates are lighter they 'float' on top of the oceanic plates. But how did they get there?
I don't know if I'm right that islands like Iceland is made of the oceanicp plate because it is in middle of the oceanic plates? But did all 'countries' start like that? It doesn't seem so as most countries/continents are made of lighter material. So how did that lighter material get on top of the oceanic plate?
The explanation of an other answer was: ' This is because the magma that solidifies to form each of these crusts travels, by partially melting its way up, through different materials and different thicknesses. The consequence of this is that the crust making up the continents is less dense than that making up the bottom of the oceans.'
Does this mean that the magma comming from beneath (hotspot etc.) is getting mixed with different materials? Or is this magma already a mix of different material where the heavier ones would stay more or sink at the bottom of the solidifieing two plates? But what makes the upper one not tight joined or gradually to the one beneath?