EARTH × EVOLUTION

Two Americas Become One

~2.8 million years ago (contested)

Phanerozoic · Cenozoic · Neogene · Pliocene

A chain of volcanic islands rose, the seaways between them narrowed, and about 2.8 million years ago the last of them closed. Animals crossed in both directions after fifty million years apart, and the Atlantic and the Pacific were separated for good.

Why it matters

Two continental faunas met and one largely replaced the other, which makes this the largest natural experiment in invasion biology we have. It matters that the closure was gradual rather than sudden: the land emerged and the water narrowed over millions of years, so the exchange had been leaking across long before the bridge was finished.

Dating & uncertaintyDisputed

A synthesis of geology, fossils and molecular data puts the final closure at 2.8 million years ago. Two published comments reject that date, arguing from the same kinds of evidence for land connections tens of millions of years earlier. The exchange is unresolved.

Sources

1. O'Dea et al. (2016), Science Advances · Formation of the Isthmus of Panama
2. Bacon et al. (2015), PNAS · Biological evidence supports an early and complex emergence of the Isthmus of Panama
3. Jaramillo et al. (2017), Science Advances · Comment on Formation of the Isthmus of Panama

Earth history as one day

23:59:0653.3 s before midnight

if Earth’s 4.54 billion years were compressed into a single day