Geol. Soc. Am. Bull. http://doi.org/fzmwwq (2012)

The Isthmus of Panama separates the Pacific Ocean from Caribbean waters. An assessment of geological data suggests that this narrow land bridge may have started to emerge from the sea as early as 47 million years ago.

Camilo Montes at the Smithsonian Tropical Research Institute, Republic of Panama, and colleagues reconstructed the evolution of the isthmus using geological mapping, dating of igneous and sedimentary rocks, and thermochronology — a method that dates the cooling of a block of rock, and can help constrain the timing of rock uplift and exhumation. Their data suggest that a large part of the land bridge may have started to emerge above sea level up to 47 million years ago. By 23 million years ago, only a very narrow seaway remained between southern Central America and South America.

The formation and emergence of the Isthmus of Panama, previously dated to between 7 and 3.5 million years ago, has been linked to significant changes in ocean circulation and climate. An early uplift of the Isthmus of Panama challenges proposed links to the intensification of Northern Hemisphere glaciation.