Long ago, one great ocean flowed between North and South America. When the narrow Isthmus of Panama joined the continents about 3 million years ago, it also separated the Atlantic from the Pacific Ocean. If this took place millions of years earlier, as recently asserted by some, the implications for both land and sea life would be revolutionary.
A team of researchers from 23 institutions set out to re-evaluate in rigorous detail, all of the available lines of evidence—geologic, oceanographic, genetic and ecological data and the analyses that bear on the question of when the Isthmus formed.
The researchers concluded that records from marine and terrestrial fossils, volcanic and marine rocks and the genes of marine animals split by the formation of the Isthmus all tell the same story: the Isthmus of Panama formed 2.8 million years ago.
Three key pieces of evidence defined when the land bridge was finally in place:
- Analysis of the family trees of shallow-water marine animals such as fish and sand dollars from the Pacific and Caribbean (Atlantic) sides of the isthmus show genetic mixing until after 3.2 million years ago.
- Surface waters from the Pacific and Caribbean mixed until about 2.8 million years ago, as seen in deep-ocean sediments.
- Massive migrations of land animals between North and South America began sometime before 2.7 million years ago.
The timing of the connection between continents and the isolation of the Pacific and Atlantic oceans is important as it is used to estimate rates of evolutionary change, models of global oceans, the origin of modern-day animals and plants of the Americas and why Caribbean reefs became established.
The authors concluded, “Our review and new analyses aims to clarify the issue by bringing together expertise from a wide array of different lines of evidence. Given all the available evidence, we strongly caution against the uncritical acceptance of an isthmus before the Pliocene.”