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The continents of North and South America came together much earlier than previously thought, according to researchers who found evidence in rock deposits from ancient rivers in Colombia of the land bridge that connected the long-isolated landmasses. The two continents are linked at Panama, but there has been a debate about when this land bridge first appeared, with most experts placing its formation at about 3 million years ago. The new study, published on Thursday in the journal Science, presents evidence that the Panama land bridge formed at least 10 million years earlier. Until then, a deep water channel called the Central American Seaway separated the continents.
The researchers base their estimate on the presence of small grains of a mineral called zircon unearthed in ancient river bedrock in northern Colombia that originated in Panama and were 13 million to 15 million years old. These grains suggested the land bridge must have existed at that time, they said. "We contend that a bridge, perhaps a transient one, was present since 13 to 15 million years ago," said geologist Camilo Montes of Universidad de los Andes in Bogota, who led the study.
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