<P> A significant body of water ( referred to as the Central American Seaway ) once separated the continents of North and South America , allowing the waters of the Pacific and Atlantic Oceans to mix freely . Beneath the surface , two plates of the Earth 's crust were slowly colliding , forcing the Cocos Plate to slide under the Caribbean Plate . The pressure and heat caused by this collision led to the formation of underwater volcanoes , some of which grew large enough to form islands as early as 15 million years ago . Meanwhile , movement of the two tectonic plates was also pushing up the sea floor , eventually forcing some areas above sea level . </P>
when did the collision between north and south america take place
as early as 15 million years ago