<P> Over time, massive amounts of sediment (sand, soil, and mud) from North and South America filled the gaps between the newly forming islands . Over millions of years, the sediment deposits added to the islands until the gaps were completely filled . By no later than 4.5 million years ago, an isthmus had formed between North and South America . However, in April 2015, an article in Science Magazine stated that zircon crystals in middle Miocene bedrock from northern Colombia indicated that by 10 million years ago, it is likely that instead of islands, a full isthmus between the North and South American continents had already likely formed where the Central American Seaway had been previously . </P> <P> Evidence also suggests that the creation of this land mass and the subsequent warm, wet weather over northern Europe resulted in the formation of a large Arctic ice cap and contributed to the current ice age . That warm currents can lead to glacier formation may seem counterintuitive, but heated air flowing over the warm Gulf Stream can hold more moisture . The result is increased precipitation that contributes to snow pack . </P> <P> The formation of the Isthmus of Panama also played a major role in biodiversity on the planet . The bridge made it easier for animals and plants to migrate between the two continents . This event is known in paleontology as the Great American Interchange . For instance, in North America today, the opossum, armadillo, and porcupine all trace back to ancestors that came across the land bridge from South America . Likewise, bears, cats, dogs, horses, llamas, and raccoons all made the trek south across the isthmus . </P> <P> As the connecting bridge between two vast land masses, the Panamanian biosphere is filled with overlapping fauna and flora from both North and South America . There are, for example, over 978 species of birds in the isthmus area . The tropical climate also encourages a myriad of large and brightly colored species, insects, amphibians, birds, fish, and reptiles . Divided along its length by a mountain range, the isthmus's weather is generally wet on the Atlantic (Caribbean) side but has a clearer division into wet and dry seasons on the Pacific side . </P>

Panama canal links what two bodies of water