What is the basic driving force for plate movement?

What are the remains of prehistoric plants and animals called? What minerals are found in Florida? How can you test if a material is magnetic? When the acid reacts with a carbonate what are the three products? How has the earths atmosphere changed over millions of years? Is sodium bicarbonate a pure element? Where are the rift valleys on earth? What is the chemical formula of chloride of lime? Is hydrogen a reactent? How would you measure the amount of air in different soils? Which of these can become stable by losing 1 electron calcium argon sodium nitrogen oxygen chlorine? Was the interior of early earth more or less homogenous than it is today? What kind of soil does the Desert Savannah have? An organism that cannot make its own food is called a-? What are the ions in sodium chloride solution? What do most igneous sedimentary and metamorphic rock have in common? What if a potassium chlorate sample is contaminated with KCL would the experimental percent oxygen be higher or lower than the theoretical percent oxygen? Why is copper useful? Why do earthquakes happen far away from plate boundaries? Why do clouds happen?

What is the basic driving force for plate movement?