Scientists studying ancient fish teeth have now proposed that the passageway where the Pacific and Atlantic oceans join began opening around 41 million years ago, much earlier than originally estimated.

In spite of being the size of a grain of sand, fossil fish teeth have a wealth of a rare Earth element known as neodymium (Nd). The isotopic ratio of this element varies from ocean to ocean. The Pacific and Atlantic oceans have a significant difference in Nd ratios. "The presence of neodymium with a Pacific signature in the deep Atlantic suggests that Pacific surface waters flowed into the South Atlantic, where they cooled and sank," explained Ellen E. Martin, study team member and associate professor of geology at University of Florida.

Gondwana, the southern supercontinent, combined the land of most of the continents in the Southern Hemisphere. About 160 million years ago, the same mechanisms that drive plate tectonics dented into the land. The dent grew and eventually became the Drake Passage, the body of water where the Atlantic and Pacific oceans meet between South America and Antarctica.

"The merging of the two oceans created a ring of cold water forming the largest ocean current in the world known as Antarctic Circumpolar Current (ACC)," said Howie Scher of University of Rochester and a study team member. The current, circling Antarctica, led to Antarctic's frigid conditions after separating it from warmer climates. Ice sheets quickly appeared in the continent about 34 million years ago.

However, the debate continues on when the ACC formed. Prior to its formation, Antarctic's temperatures most likely included the subtropical surface currents. "This transport of heat would have been interrupted as the ACC began to circulate following the opening of passageways around Antarctica," Scher told meryl.net.

Searching for Clues in Fish Teeth and Rare Cruises

While on a different project, Martin found and analyzed fish teeth, which are made from the same material as human teeth. Scher and Martin verified the reliability of fossilized fish teeth for a better estimate of when the opening of the Drake Passage occurred. "The idea was to use a sediment core from the Atlantic Ocean to determine the earliest appearance of the isotopic signature of Pacific seawater, which would mark the opening of Drake Passage," Scher said.