Over a hundred years ago, laborers rectified an inconvenience imposed by geology some millions of years before by digging the Panama Canal. The less-than-one-hundred-kilometer-wide Isthmus of Panama was all that blocked the way of ships wishing to travel between the Atlantic and Pacific Oceans without an outrageous detour.
The waters of those oceans could lodge the same complaint. Before Panama was there, currents would have connected the two oceans near the equator, producing a profoundly different pattern of ocean circulation from what we see today. At the same time the thin land bridge connected the long-separated organisms of North and South America, releasing terror birds into North America and horses into South America, for example.
So when did all this happen? That’s not an easy question to answer. Our best guess was that it had occurred 3 to 4 million years ago, coinciding with fossil evidence of species migrations, changes in the salinity of the Caribbean Sea, and a transition from the warm Pliocene climate toward a Pleistocene defined by ice sheets.
Read 10 remaining paragraphs | Comments
No comments:
Post a Comment