If your floor really needs more than that, consider a low-cost alternative to refinishing: Apply a fresh topcoat of nonyellowing polyurethane, found in the flooring section of a home improvement store. Be sure to very lightly sand the floors with a pole sander and fine-grit sandpaper.
There are 440 different species of sharks in the world today classified into eight different orders described below with some examples of known sharks species for each group.
Each shark can produce up to 30,000 teeth over the span of their life. These teeth consist of dentine and enamel which does fossilize in the ocean. There are ways to determine how old these teeth are. That has lead to significant evidence of how long sharks have been around.