New age for Panama closure challenges long-held theories
PULLMAN, Wash. – The Panama Isthmus is so strategic that more than 100 years ago global powers France and the United States took on the monumental task of constructing the Panama Canal. They sought to shorten transit times between Asia, Europe and the Americas by re-joining the Pacific and Caribbean seas. If you want to rule the world, Panama is crucial.
But new research published in the journal Science suggests Panama has not always been so important, at least not for mammal evolution and global climate. Until now, the scientific consensus was that the isthmus closed about 3 million years ago. This joined the Americas – allowing migration of land animals between them – separated the Pacific and Caribbean seas and changed global climate.
The new data suggests closure may have taken place much earlier, between 13 and 15 million years ago. If this is so, the role of Panama closure in those global processes is inconsequential. It also means that the reasons underlying those global processes need to be reevaluated.
Closure of the isthmus affected global climate by rerouting ocean currents in both the Atlantic and Pacific. This affected evaporation, rainfall, humidity and ocean salinity and circulation – all with worldwide repercussions.
Camilo Montes, from Universidad de los Andes in Bogotá, Colombia, and Victor A. Valencia, a part time researcher in Washington State University’s School of the Environment, analyzed zircon grains – a mineral ubiquitous in Earth’s crust – in ancient sea and river beds in northwestern South America. They found that ancient beds younger than about 13 to 15 million years contain abundant zircon grains with a typically Panamanian age.
Older beds contain none. The researchers and several colleagues interpreted this as being from the time Panama docked to South America, nearly 10 million years before the traditionally accepted age of closure.
The analytical work was performed in WSU’s radiogenic lab using laser ablation technology, which has a laser beam vaporize a sample for spectroscopic analysis to get isotopic ratios that are used as ages. Advances in the field let the researchers do analyses that, 15 years ago, “would have taken years to perform,” said Valencia.
The incredible endurance of zircon to weathering and erosion brings new oxygen to the Panama debate. These tiny grains debunk the closure of the Panama Isthmus as the main cause for global climatic change and the American biotic exchange. What is left is to re-think what other processes could have been responsible for those global changses nearly 3 million years ago.
Victor A Valencia, WSU School of the Environment, firstname.lastname@example.org