Isthmus of Panama

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The Isthmus of Panama is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It was formed some 3 million years ago during the Pliocene epoch. It contains the nation of Panama and the Panama Canal. Like many isthmuses, it is a location of great strategic value.

[edit] Geology

Before the present-day isthmus was created, water covered the area where Panama is today. There was a gap between the continents of North and South America through which the waters of the Atlantic and Pacific Oceans flowed freely. Beneath the surface, two plates of the Earth's crust were slowly colliding, forcing the Pacific Plate to slide under the Caribbean Plate. The pressure and heat caused by this collision led to the formation of underwater volcanoes, some of which grew large enough to form islands as early as 15 million years ago. Meanwhile, movement of the two tectonic plates was also pushing up the sea floor, eventually forcing some areas above sea level.

Over time, massive amounts of sediment (sand, soil, and mud) from North and South America filled the gaps between the newly forming islands. Over millions of years, the sediment deposits added to the islands until the gaps were completely filled. By about 3 million years ago, an isthmus had formed between North and South America.

Scientists believe the formation of the Isthmus of Panama is one of the most important geologic events in the last 60 million years. Even though only a small sliver of land relative to the sizes of continents, the Isthmus of Panama had an enormous impact on Earth's climate and its environment. By shutting down the flow of water between the two oceans, the land bridge re-routed ocean currents in both the Atlantic and Pacific Oceans. Atlantic currents were forced northward, and eventually settled into a new current pattern that we call the Gulf Stream today. With warm Caribbean waters flowing toward the northeast Atlantic, the climate of northwestern Europe grew warmer. (Winters there would be as much as 10° C colder in winter without the transport of heat from the Gulf Stream.) The Atlantic, no longer mingling with the Pacific, grew saltier. Each of these changes helped establish the global ocean circulation pattern in place today. In short, the Isthmus of Panama directly and indirectly influenced ocean and atmospheric circulation patterns, which regulated patterns of rainfall, which in turn sculpted landscapes.

Evidence also suggests that the creation of this land mass and the subsequent, warm wet weather over northern Europe resulted in the formation of an Arctic ice cap and contributed to the ice age during the following Pleistocene Epoch.

The formation of the Isthmus of Panama also played a major role in biodiversity on the planet. The bridge made it easier for animals and plants to migrate between the two continents. For instance, in North America today, the opossum, armadillo, and porcupine all trace back to ancestors that came across the land bridge from South America. Likewise, ancestors of bears, cats, dogs, horses, llamas, and raccoons all made the trek south across the isthmus.

[edit] Biosphere

As the connecting bridge between two vast land masses the Panamanian biosphere is crammed with overlapping fauna and flora from both North and South America. There are, for example, over 500 species of birds in the isthmus area. The tropical climate also encourages a myriad of large and brightly coloured species: insects, snakes, fish and reptiles. Divided along its length by a mountain range, the isthmus's weather is generally wet on the Atlantic / Caribbean side but has a clearer division into wet and dry seasons on the Pacific side.

[edit] References

• Panama: Isthmus that Changed the World. NASA Earth Observatory. Retrieved on 2006-05-30.

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