The quotation from the article:
"The formation of volcanoes at the edges of plates is closely tied to the
movement of tectonic plates, which are created as hot magma pushes up
through fissures in mid-ocean ridges and solidifies. As the plates move
away from the ridges, they cool, harden and get heavier, eventually sinking
back down into the mantle at subduction zones."
What if a young curious mind would read the text and ask the next
questions:
***
1. How a plate getting heavier makes it to sink down. The thing should
develop its density to sink down.
2. Is a plate really cooling? The top and bottom border conditions for
temperature remain the same. The plate develops its thickness, Its
"average" temperature remains aprox the same.
3. The coefficient of thermal expansion of the material a plate is built of
is the smallest. Combined with the fact that the plate does not cool make
the plate density to be stable. Why is the plate eventually sinking back
down into the mantle when the plate's density is stable?
4. If an elementary volume of mantle develops its density on cooling and
changing its state to solid, - why does it glue to the ceiling (a plate's
bottom), why not it to drop down just on the cooling.
***