Which of the following is considered the most important and yet most threatened ecosystem on the planet? coastal wetlands rainforests coastal ranges argentinian pampas 9. why are there so many earthquakes in south america? south america’s incredible biodiversity lends itself to hazardous conditions. south america’s location atop the nazca and south american plates of the circum-pacific belt. south america’s lack of stable infrastructure and good building codes. south america’s proximity to two major oceans and the equator.