2007-01-13 03:23:26 · 3 answers · asked by TeganMc 2 in Science & Mathematics ➔ Earth Sciences & Geology
its all about plate techtonics.(movement of plates on the crust of the earth).as the plates of the earth have moved over the 3.6 billion years that the earth has been around the lighter "oceanic" crust has been continually "subducted" or pushed under the continental or land crust and melted thus the older ocean floor has gone and is continually being formed from the mid atlantic ridge.read up on plate tectonics and that will explain it clearer than i have!
2007-01-13 03:41:57 · answer #1 · answered by susan t 2 · 0⤊ 0⤋
Because they are constantly being renewed. They spread from the mid-ocean ridges. As they are heavier than the rock that makes up the continents, they are subducted, and go back down into the mantle. That's the short answer. There is a lot more to the whole process. Read about it. It's absolutely fascinating. All the continents and ocean floors are constantly in motion, which is why we have earthquakes and volcano's.
2007-01-13 08:52:59 · answer #2 · answered by Anonymous · 0⤊ 0⤋
it due to subduction and they the fact that are lighter due to their mineral composition
2007-01-15 07:24:56 · answer #3 · answered by dottydog 4 · 0⤊ 0⤋