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 those seaways closed. Animals crossed in both directions after fifty million years of separation, and the Atlantic and the Pacific were cut off from each other for good.

Why it matters

Two continental faunas met and mixed, and the turnover that followed is one of the largest natural experiments in invasion biology we have. The closure was gradual rather than sudden, and that matters: the land emerged and the water narrowed over millions of years, so the exchange had been leaking across well 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 many millions of years earlier. The timing 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