Which continent has the highest elevation and lowest?

There is no data available for "average elevations of continents" except that Antarctica, with its deep ice cap, has the highest overall elevation. This would not be the case if considering the underlying land surface. Of the 7 classic continents, Australia (proper) may have the lowest elevation because it has fewer tall mountain ranges than Europe or the Americas.

Asia has the lowest and highest points on earth, the Dead Sea on Israel/Jordan border is the lowest and the highest is Mount Everest, Nepal/China