The primary force that causes the seafloor to spread and continents to drift is the heat energy of the core.
The main cause of continental drift and sea floor spreading is the heat energy that comes out from the core portion of the earth. The earth's outer shell is composed of plates that move a little every year.
Heat coming from the interior of the earth triggers this movement to occur through convection currents inside the mantle so we can conclude that heat energy is responsible for the seafloor to spread and continents to drift
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