When Were the Atlantic and Pacific Oceans Separated by Land?
ES2307  Dating the Formation of the Isthmus of Panama

By examining the collections of microfossils, you can see that Pulleniatina is present in sediments only on the Pacific side and only in the more recent layers of sediments. Pulleniatina is an example of an organism that had been isolated from other groups of foraminifera, then diverged to become an entirely new species.

At some stage in Earth's geological history, a land bridge formed, connecting Central and South America and closing off the Caribbean Sea from the Pacific Ocean. Pulleniatina was a species that developed in the new conditions of the Pacific Ocean. It did not have an opportunity to spread to the Caribbean side because the land bridge was in the way.

You’ve examined evidence that a land bridge formed, separating the Caribbean Sea and the Pacific Ocean. From the data you’ve collected, what can you infer about the timing of the formation of the land bridge? Use your chart showing the presence/absence of Pulleniatina and the animation of plate movement to determine the most likely date that the isthmus was formed.

Movement of land masses and uplift of submerged land between Central and South America from 6 million years ago to 2.5 million years ago.

8. How many years ago was the Isthmus of Panama formed? Explain how you used the data to determine this.

9. Summarize the changes that have occurred in Earth's spheres on either side of the Isthmus of Panama from six to three million years ago.



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