Land bridge between North and South America older than thought

Ars Technica : Exactly how many millions of years ago the continents of North and South America became joined by the Isthmus of Panama has been difficult to determine. Previous estimates have been based on such factors as fossil evidence of species migrating between the two continents and changes in the Caribbean Sea’s salinity. To fine-tune the timeline, Camilo Montes of the University of Los Andes and colleagues studied grains of the mineral zircon embedded in igneous rock in Panama and neighboring Colombia. Zircon is incredibly durable and contains trace amounts of uranium, which can be used for radiometric dating. The researchers found that while the igneous rock, and hence the zircon, in Colombia were much older than those in Panama, there was evidence of Panamanian zircon embedded in younger sedimentary rock in Colombia. They propose that as the two countries joined up, rivers carried sediment from Panama to Colombia. What was surprising was that the flow appears to have started about 14 million years ago—some 10 million years earlier than previous estimates for the joining of the two continents.