When the isthmus emerged and halted the exchange of water between the Atlantic and the Pacific, salinity in the former rose, depleting the Caribbean of certain nutrients, making the water more crystalline and giving birth to the coral reefs for which the sea is known. This denser water helped give rise to the global ocean conveyor belt, in which warm, fresh water is transported north and cooler salty water flows south of the equator and on to Antarctica, where it warms the cold bottom waters and helps them rise to the surface. The system distributes heat and moisture around the planet.
The implications of the project are vast for the scientific community, but for the investigators combing through the banks of the canal, the experience carries overwhelming personal weight. “This is 21 million years old, and I’m the first person to see it,” said Colleary, 29, clutching a rock that might have a fossil embedded in it. “That’s what gets to me.”
Maccracken’s eyes sparkle as she reminisces about the fossils she has found, including the toe of a giant beardog, an extinct dog-like animal that was as big as a black bear and which migrated to the isthmus from North America. Other investigators have found fossilized remains of miniature camels, horses, monkeys, rhinos, caimans and bats. Fossils of fruits and flowers have also been found, revealing a forest with tropical elements, says Jaramillo. Many of these contain a mixture of elements from North America and South America.