How does seafloor spreading provide further evidence of continental drift

Tectonic plates is caused by the immense heat of the earth's core that travel's through convection. 

A convergent boundary is a destructive plate boundary. It is a region where two or more tectonic plates move towards each other and collide. A good example of this is the San Andreas fault off the West Coast of America. When these plates collide, they can either cause an earthquake or a volcano to erupt. The intensity of the earthquake or volcano eruption depends on the speed at which the tectonic plates collide

A. they hold atoms  together with a molecule.its a force that exist between molecules. hope this .

Independent variable is something that is changed in a experiment.