Scientists find a firm date for when the Atlantic and Pacific Ocean divided: 2.8 million years ago. Carlos Jasso/Reuters

Once upon a time, the Atlantic Ocean and the Pacific Ocean were one body of water without separate names or identities. The oceans parted millions of years ago when the Isthmus of Panama joined North and South America, creating a divide in the water and the two isolated oceans we know today.

When the two bodies of water formed has been debated in the scientific community, with some estimates suggesting 23 million years ago and others saying it took place six million years prior. Researchers at the Smithsonian Tropical Research Institute (STRI), led by staff scientist Aaron O'Dea, have found a firm date for the partition of the ocean: 2.8 million years ago.

"Recent scientific publications proposing the isolation of the two oceans between 23 to 6 million years ago rocked the generally held model of the continental connection to its foundations," said Jeremy Jackson, emeritus staff scientist at the Smithsonian, in a statement. "O'Dea and his team set out to reevaluate in unprecedented, 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."

To settle on this date, the team of researchers from 23 institutions analyzed the family trees of shallow-water marine animals (e.g. fish, sand dollars) in the Pacific and Atlantic oceans. The analysis showed genetic mingling until after 3.2 million years ago. A similar look at surface waters showed genetic mixing until 2.8 million years ago. Analyzing the migrations of land animals between North and South Americans dates the massive relocations to before 2.7 years ago.

“Our review and new analyses aims to clarify the issue by bringing together expertise from a wide array of different lines of evidence,” conclude the authors, who published their findings in Science Advances. “Given all the available evidence, we strongly caution against the uncritical acceptance of the old isthmus hypothesis."

The timeline of when the two oceans were created is an important fact to know, as it would shed insight on how things transpired for land and sea life in the years to follow.

"The timing of the connection between continents and the isolation of the Pacific and Atlantic oceans is important for so many reasons," O'Dea said. "Estimates of 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 all depend upon knowing how and when the isthmus formed."