A thin strip of land rising from the sea rerouted the planet's ocean currents

Around 3 million years ago, tectonic activity finally closed the last gap between North and South America, forming the Isthmus of Panama and splitting one ocean into the Atlantic and Pacific. The new land bridge let species migrate between continents that had been separate for tens of millions of years, and rerouted ocean currents in a way some scientists link to the start of Northern Hemisphere ice ages.

— Wikipedia contributors, Isthmus of Panama — Great American Biotic Interchange