Because salinity (in concert with temperature) affects the density of seawater, it can play a role in its vertical stratification. Essentially, lower salinity water (= lower density) floats on top of higher salinity water (= higher density).
Alternative definition, a choice limited to one of two or more possibilities, as of things, propositions, or courses of action, the selection of which precludes any other possibility: You have the alternative of riding or walking. See more.
Best answer: Well... multiple reasons in theory. Some think we exist, because of random chance that lead to the lucky development of the human race. Some think an outside source like aliens or god may be the reason to why we exist. Some think we exist with a reason we have yet to find out until the future.