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The Isthmus of Panama.

The Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking Central 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.

Núñez de Balboa's travel route to the South Sea, 1513.

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Vasco Núñez de Balboa heard of the South Sea from the natives while sailing along the Caribbean coast. On September 25, 1513 he saw the Pacific.

Silver and gold from the viceroyalty of Peru were transported overland across the isthmus to Porto Bello where Spanish treasure fleets shipped them to Seville (Cádiz from 1707).

Lionel Wafer spent four years between 1680 and 1684 among the Cuna Indians.

Scotland tried to establish a settlement in 1698 through the Darien scheme.

Ferdinand de Lesseps, the man behind the Suez Canal, started a Panama Canal Company in 1880 that went bankrupt in 1889 in a scandal.

In 1902–04 the United States forced Colombia to grant independence to the department of the Isthmus and bought the remaining assets of the PCC and finished the canal in 1914.

Before the present-day isthmus was created, water covered the area where Panama is today. A significant body of water (referred to as the Central American Seaway) separated the continents of North and South America, allowing the waters of the Pacific and Atlantic Oceans to mix 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. This event is known in paleontology as the Great American Interchange. 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.

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.

• Panama: Isthmus that Changed the World. NASA Earth Observatory.

• A New Voyage and Description of the Isthmus of America (1695), by Lionel Wafer. Excerpt from the 1729 Knapton edition.

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