New Study Reaffirms Timeline On Formation Of Isthmus Of Panama

The formation of the Isthmus of Panama - a strip of land that separates the Caribbean Sea from the Pacific Ocean, and connects North and South America-- is considered one of the most important geologic, oceanographic, and biogeographic events ever, but the exact timing of the final closure of the Isthmus has become controversial. A relatively recent date for the closure, approximately 3 million years ago, has been the consensus among the scientific community for decades, but new research shows that the closure happened much earlier, as much as 23 million years ago.

A team of international scientists that includes professors Ron Eytan, assistant professor in Marine Biology at the Texas A&M's Galveston campus and E.L. Grossman of Texas A&M's Department of Geology and Geophysics in College Station, Texas reaffirms the traditional consensus of a recent closure, and firmly disproves the hypothesis of an early closure of the Isthmus of Panama.

Estimated dates for the formation of the Isthmus of Panama go back as far as 15 million years ago, but in the 1970s it was universally agreed that the Isthmus (defined as a narrow portion of land enclosed on each side by water and connecting two larger bodies of land) was formed about 3 million years ago. In this new paper, using geological, paleontological and molecular genetics, among other methods the team has pinpointed the formation date to 2.8 million years ago.

The timing of the closure is important for a multitude of reasons, such as how new species form, understanding genome evolution, models of global ocean circulation, the origin of modern fauna and flora in the Americas and how Caribbean reefs became established.

Eytan, an evolutionary geneticist, studies marine fishes. He worked with colleagues to assemble and analyze the molecular genetics portion of the paper. He explains, "The separation of the Pacific Ocean and what would become the Caribbean Sea by the Isthmus has been called 'The Great American Schism'. This is because marine taxa suddenly had their routes of migration blocked and gene flow between populations could no longer occur due to the closure of the Isthmus. This in turn led to the formation of new species on either side of the Isthmus thus generating novel marine biodiversity."

"The timing of the closure of the Isthmus has been used to calibrate a 'molecular clock', Eytan adds. "This clock has been used in hundreds of studies to infer the timing of speciation and how long ago populations of plants and animals have been separated from one another. The new hypotheses of an 'early closure' would have upended all of these studies and called into question what we know about molecular evolution, speciation and the timing of the assembly of ecological communities."

"It's been proved that the creation of the Isthmus of Panama is also directly responsible for changes in the Earth's climate and weather patterns over millions of years," says Eytan.

"As the plates of the Earth's crust were slowly colliding with each other and the Isthmus was being formed, it altered ocean currents, even changing direction for some of them and eventually affected water temperatures. By altering the flow of water between the two oceans, we know that the Isthmus of Panama contributed to the formation of the Gulf Stream, which covers much of the Atlantic and its warm waters affect weather and precipitation" says Eytan. "So you could say the Isthmus directly and indirectly influenced ocean patterns, weather patterns and atmospheric conditions which in turn shaped landscapes over a wide area of the world."

It also affected worldwide commerce - the opening of the Panama Canal in 1914, considered one of mankind's greatest engineering achievements through the Isthmus, forever changed world trade and the economies of numerous countries.

Eytan and Grossman, along with colleagues from the Smithsonian Tropical Research Institute, the University of Florida, the Universidad Nacional de Colombia, the University of Nevada, Florida International University, Scripps Institution of Oceanography, the U.S. Geological Survey, Rutgers University, the University of California-Riverside, the University of Iowa, Hamilton College, the University of California-Berkeley, the Natural History Museum, the Woods Hole Oceanographic Institution, Washington and Lee University, the University of Hawaii and the University of California-Davis have had their work published in the latest issue of Science Advances.

The project was funded by the National Science Foundation, the Smithsonian Tropical Research Institute, the U.S. Geological Survey, and various scientific offices from countries of Panama and Argentina.