The Isthmus of Panama

The Isthmus of Panama (Spanish: Istmo de Panamá), also historically known as the Isthmus of Darien (Istmo de Darién),[1][2] is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country of Panama and the Panama Canal. Like many isthmuses, it is a location of great geopolitical and strategic importance.

The isthmus is thought to have been finally formed around 3 million years ago (Ma),[3] separating the Atlantic and Pacific Oceans and causing the creation of the Gulf Stream, as first suggested in 1910 by Henry Fairfield Osborn. Osborn based the proposal on the fossil record of mammals in Central America,[4] a conclusion that would provide a foundation for Alfred Wegener when he proposed the theory of continental drift in 1912.[5] Some recent studies[6][7][8] suggest an earlier formation of the isthmus than the recognized age of 3 Ma, potentially stretching as far back as 19 Ma.[9]


Main article: History of Panama

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

Vasco Núñez de Balboa heard of the South Sea from natives while sailing along the Caribbean coast.[10] On 25 September 1513 his expedition became the first Europeans to see the Pacific Ocean from the Americas. In 1519 the town of Panamá was founded near a small indigenous settlement on the Pacific coast. After the Spanish colonization of Peru, it developed into an important port of trade and became an administrative centre. In 1671 the Welsh privateer Henry Morgan crossed the Isthmus of Panamá from the Caribbean side and destroyed the city. The town was relocated some kilometers to the west at a small peninsula. The ruins of the old town, Panamá Viejo, are preserved and were declared a UNESCO World Heritage Site in 1997.

Silver and gold from the viceroyalty of Peru were transported overland across the isthmus by the Spanish Silver Train to Porto Bello, where Spanish treasure fleets shipped them to Seville and Cádiz from 1707. Lionel Wafer spent four years between 1680 and 1684 among the Kuna or Guna Indians.[11] Scotland tried to establish a settlement in 1698 through the Darien scheme.

An 1850 oil painting by Charles Christian Nahl: The Isthmus of Panama on the Height of the Chagres River

The California Gold Rush, starting in 1849, brought a large increase in the transportation of people from the Atlantic to the Pacific. Steamships brought gold diggers from eastern U.S. ports, who trekked across the isthmus by foot, horse, and later rail. On the Pacific side, they boarded Pacific Mail Steamship Company vessels headed for San Francisco.[citation needed]

Ferdinand de Lesseps, the developer of the Suez Canal, started a Panama Canal Company in 1880 that went bankrupt in 1889 in the Panama scandals. In 1902–1904, the United States forced Colombia to grant independence to the Department of the Isthmus, bought the remaining assets of the Panama Canal Company, and finished the canal in 1914.[citation needed]


The closure of the Isthmus led to allopatric speciation events of marine organisms isolated on each side (blue and green). Terrestrial species also migrated between the two continents (the Great American Biotic Interchange) upon the formation of a passable land bridge.

A significant body of water (referred to as the Central American Seaway) once 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 Cocos 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. Meanwhile, movement of the two tectonic plates was also pushing up the sea floor, eventually forcing some areas above sea level.

The Isthmus of Panama is not the only part of central America that has been low lying in the last tens of million years. This means the date of first closure and final closure of the Central American Seaway before it was artificially reopened to a degree by the Panama Canal is likely to remain controversial as noted by those who proposed 15 Ma for first closure except for narrow passages on geological grounds[12] and suggestions that final closure might be more recent based on genetic drift data of black mangroves along the Atlantic and Pacific coasts.[13][relevant?]

Over time, massive amounts of sediment 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 gap was completely filled. By no later than 4.5 Ma, an isthmus had formed between North and South America.[citation needed] However, an article in Science magazine stated that zircon crystals in middle Miocene bedrock from northern Colombia indicated that by 10 Ma, it is likely that instead of islands, a full isthmus between the North and South American continents had already formed where the Central American Seaway had been previously.[14] A genomic study of army ants also suggests that the isthmus emerged millions of years earlier than had long been thought.[15]

However the process of formation of the isthmus and its implications is geologically and ecologically more nuanced. There is isotopic and carbonate deposition rate evidence that deep water connections below 1,800 m (5,900 ft) were broken between the Atlantic and Pacific by between 12 and 9.2 Ma.[3] However exchange of surface water so as to maintain western Atlantic salinity at eastern Pacific values continued until about 4.6 Ma with current Caribbean values being reached by about 4.2 Ma although there seems to have been a last definite temporary breach as recently as 2.45 Ma.[3][16] The ocean sediments between the volcanoes on the isthmus seem to have been laid down as recently as 3.1 Ma and the exchange of organism gene pools between the two oceans appears to have continued until about 3 Ma as well.[3] The largest exchange of animals over the land bridge only happened after this time, although some species had made the crossing earlier, perhaps by rafting or brief periods of connection separated by periods of a high water flow between an arc of volcanic islands not conducive to swimming or rafting.[3]

Group of people making their way through the jungle on horseback. One man has fallen in the water, another is pulling a dog on a leash
Francis Samuel Marryat, Crossing The Isthmus Of Panama, 1855

Evidence also suggests that the creation of this land mass and the subsequent warm, wet weather over northern Europe resulted in the formation of a large Arctic ice cap and contributed to the current ice age. That warm currents can lead to glacier formation may seem counterintuitive, but heated air flowing over the warm Gulf Stream can hold more moisture. The result is increased precipitation that contributes to snow pack.[citation needed]

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, the opossum, armadillo, and porcupine all trace back to ancestors that came across the land bridge from South America. Likewise, 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 filled with overlapping fauna and flora from both North and South America. There are, for example, over 978 species of birds in the isthmus area.[17] The tropical climate also encourages a myriad of large and brightly colored species, insects, amphibians, birds, 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.

See also



  1. ^ "BBC - History - British History in depth: The Darien Venture".
  2. ^ "The Darien Scheme". Historic UK.
  3. ^ a b c d e O'Dea, A.; Lessios, H. A.; Coates, A. G.; Eytan, R. I.; Restrepo-Moreno, S. A.; Cione, A. L. (2016). "Formation of the Isthmus of Panama". Science Advances. 2 (8): e1600883. Bibcode:2016SciA....2E0883O. doi:10.1126/sciadv.1600883. PMC 4988774. PMID 27540590.
  4. ^ Osborn 1910, pp. 80–81
  5. ^ Wegener 2003.
  6. ^ Bacon, Christine D.; Silvestro, Daniele; Jaramillo, Carlos; Smith, Brian Tilston; Chakrabarty, Prosanta; Antonelli, Alexandre (12 May 2015). "Biological evidence supports an early and complex emergence of the Isthmus of Panama". Proceedings of the National Academy of Sciences. 112 (19): 6110–6115. doi:10.1073/pnas.1423853112. PMC 4434730. PMID 25918375.
  7. ^ Hoorn, Carine; Flantua, Suzette (10 April 2015). "An early start for the Panama land bridge". Science. 348 (6231): 186–187. doi:10.1126/science.aab0099. PMID 25859033. S2CID 30231555.
  8. ^ Montes et al. 2015.
  9. ^ Donovan, Kelly (20 March 2009). "Isthmus of Panama formed as result of plate tectonics". Florida Museum of Natural History.
  10. ^ Andagoya, Pascual de (21 June 1865). "Narrative of Pascual de Andagoya". Narrative of the Proceedings of Pedrarias Davila. The Hakluyt Society – via Wikisource.
  11. ^ Wafer 1729
  12. ^ Coates, Anthony G; Stallard, Robert F (2013). "How old is the Isthmus of Panama?" (PDF). Bulletin of Marine Science. 89 (4): 801-813. doi:10.5343/bms.2012.1076.
  13. ^ Ochoa-Zavala, Maried; Jaramillo-Correa, Juan Pablo; Piñero, Daniel; Nettel-Hernanz, Alejandro; Núñez-Farfán, Juan (2019). "Contrasting colonization patterns of black mangrove (Avicennia germinans (L.) L.) gene pools along the Mexican coasts". Journal of Biogeography. 46 (5): 884–898. doi:10.1111/jbi.13536. S2CID 109795658.
  14. ^ Montes et al. 2015
  15. ^ Golembiewski, Kate (25 October 2016). "Ant Genomics Help Reshape Biological History of the Americas". Retrieved 8 January 2022.
  16. ^ Grossman, Ethan L.; Robbins, John A.; Rachello-Dolmen, Paola G.; Tao, Kai; Saxena, Divya; O’Dea, Aaron (2019). "Freshwater input, upwelling, and the evolution of Caribbean coastal ecosystems during formation of the Isthmus of Panama". Geology. 47 (9): 857–861. Bibcode:2019Geo....47..857G. doi:10.1130/G46357.1. S2CID 199095294.
  17. ^ Angehr & Dean 2010

General sources

8°40′N 80°0′W / 8.667°N 80.000°W / 8.667; -80.000