Plate Tectonics: Outer Layers of the Earth

The theory of plate tectonics (meaning "plate structure") was developed in the 1960's. This theory explains the movement of the Earth's plates (which has since been documented scientifically) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon.

The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Most of the Earth's seismic activity (volcanoes and earthquakes) occurs at the plate boundaries as they interact. 

The top layer of the Earth's surface is called the crust (it lies on top of the plates). Oceanic crust (the thin crust under the oceans) is thinner and denser than continental crust. Crust is constantly being created and destroyed; oceanic crust is more active than continental crust.
Under the crust is the rocky mantle, which is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. The upper mantle is rigid and is part of the lithosphere (together with the crust). The lower mantle flows slowly, at a rate of a few centimeters per year. The asthenosphere is a part of the upper mantle that exhibits plastic properties. It is located below the lithosphere (the crust and upper mantle), between about 100 and 250 kilometers deep.

Plate Tectonics: Earth's Major Plates

The current continental and oceanic plates include: the Eurasian plate, Australian-Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos plate, North American plate, Caribbean plate, South American plate, African plate, Arabian plate, the Antarctic plate, and the Scotia plate. These plates consist of smaller sub-plates. 

The theory of plate tectonics (meaning "plate structure") was developed in the 1960's. This theory explains the movement of the Earth's plates (which has since been documented scientifically) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon.

The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Most of the Earth's seismic activity (volcanoes and earthquakes) occurs at the plate boundaries as they interact. 

The top layer of the Earth's surface is called the crust (it lies on top of the plates). Oceanic crust (the thin crust under the oceans) is thinner and denser than continental crust. Crust is constantly being created and destroyed; oceanic crust is more active than continental crust.

Under the crust is the rocky mantle, which is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium. The upper mantle is rigid and is part of the lithosphere (together with the crust). The lower mantle flows slowly, at a rate of a few centimeters per year. The asthenosphere is a part of the upper mantle that exhibits plastic properties. It is located below the lithosphere (the crust and upper mantle), between about 100 and 250 kilometers deep. 

All About Plate Tectonics: Earth's Plates and Continental Drift

The Earth's rocky outer crust solidified billions of years ago, soon after the Earth formed. This crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle. 

The plates are made of rock and drift all over the globe; they move both horizontally (sideways) and vertically (up and down). Over long periods of time, the plates also change in size as their margins are added to, crushed together, or pushed back into the Earth's mantle. These plates are from 50 to 250 miles (80 to 400 km) thick.


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The map of the Earth is always changing; not only are the underlying plates moving, but the plates change in size. Also, the sea level changes over time (as the temperature on Earth varies and the poles melt or freeze to varied extents), covering or exposing different amounts of crust.

Magellan's Voyage

This portolan map shows Magellan's remarkable voyage around the world from 1519 to 1521. The map is hand drawn and painted on vellum. It was prepared by a Genoese chart maker, Battista Agnese and produced in Venice. A "portolan" map is the earliest style of nautical chart and Agnese prepared a number of remarkably accurate and beautifully decorated charts of this style.

Magellan's voyage led to Limasawa, Cebu, Mactan, Palawan, Brunei, Celebes and finally to the Spice Islands.

1520: Mutiny on Magellan’s Expedition

For overwintering, Magellan established a temporary settlement called Puerto San Julian on March 30, 1520. On Easter (April 1 and 2), a mutiny broke out involving three of the five ship captains. 

Magellan took quick and decisive action. Luis de Mendoza, the captain of Victoria, was killed by a party sent by Magellan, and the ship was recovered. After Concepcion's anchor cable had been secretly cut by his forces, the ship drifted towards the well-armed Trinidad, and Concepcion's captain de Quesada and his inner circle surrendered. 

Juan de Cartagena, the head of the mutineers on the San Antonio, subsequently gave up. Antonio Pigafetta reported that Gaspar Quesada, the captain of Concepcion, and other mutineers were executed, while Juan de Cartagena, the captain of San Antonio, and a priest named Padre Sanchez de la Reina were marooned on the coast. Most of the men, including Juan Sebastián Elcano, were needed and forgiven. Reportedly those killed were drawn and quartered and impaled on the coast; years later, their bones were found by Sir Francis Drake.

Mendoza’s assassination. From this site.

Though Magellan made an example of the leaders, he pragmatically spared about 40 others after keeping them in chains and working the pumps for three months.

Voyage of Circumnavigation Departure and Passage into the Pacific

Departure and crossing of the Atlantic

The Strait of Magellan cuts through the southern tip of South America connecting the Atlantic Ocean and Pacific Ocean.

On 10 August 1519, the five ships under Magellan's command – Trinidad, San Antonio, Concepción, Victoria and Santiago – left Seville and descended the Guadalquivir River to Sanlúcar de Barrameda, at the mouth of the river. There they remained more than five weeks. Finally they set sail on 20 September.

King Manuel I ordered a Portuguese naval detachment to pursue Magellan, but Magellan avoided them. After stopping at the Canary Islands, Magellan arrived at Cape Verde, where he set course for Cape St. Augustine in Brazil. On 27 November the expedition crossed the equator; on 6 December the crew sighted South America.

As Brazil was Portuguese territory, Magellan avoided it and on 13 December anchored near present-day Rio de Janeiro. There the crew was resupplied, but bad conditions caused them to delay. Afterwards, they continued to sail south along South America's east coast, looking for the strait that Magellan believed would lead to the Spice Islands. The fleet reached Río de la Plata on 10 January 1520.

For overwintering Magellan established a temporary settlement called Puerto San Julian on March 30, 1520. On Easter (April 1 and 2) a mutiny broke out involving three of the five ship captains. Magellan took quick and decisive action. Luis de Mendoza, the captain of Victoria, was killed by a party sent by Magellan and the ship was recovered. Then, after Concepcion's anchor cable had been secretly cut, the ship drifted towards the well-armed Trinidad, and Concepcion's captain, de Quesada, and his inner circle surrendered. Juan de Cartagena, the head of the mutineers on the San Antonio subsequently gave up. Antonio Pigafetta reported that Gaspar Quesada, the captain of Concepcion, and other mutineers were executed, while Juan de Cartagena, the captain of San Antonio, and a priest named Padre Sanchez de la Reina were marooned on the coast. Most of the men, including Juan Sebastián Elcano were needed and forgiven.[16] Reportedly those killed were drawn and quartered and impaled on the coast; years later, their bones were found by Sir Francis Drake. There is a replica of the Victoria that can be visited in Puerto San Julian.
The Strait of Magellan cuts through the southern tip of South America connecting the Atlantic Ocean and Pacific Ocean.

Passage into the Pacific

The journey resumed. The help of Duarte Barbosa was crucial to face the riot in Puerto San Julian, becoming since then captain of the Victoria. The Santiago was sent down the coast on a scouting expedition and was wrecked in a sudden storm. All of its crew survived and made it safely to shore. Two of them returned overland to inform Magellan of what had happened, and to bring rescue to their comrades. After this experience, Magellan decided to wait for a few weeks more before again resuming the voyage.

At 52°S latitude on 21 October the fleet reached Cape Virgenes and concluded they had found the passage, because the waters were brine and deep inland. Four ships began an arduous trip through the 373-mile (600 km) long passage that Magellan called the Estrecho (Canal) de Todos los Santos, ("All Saints' Channel"), because the fleet travelled through it on 1 November or All Saints' Day. The strait is now named the Strait of Magellan. Magellan first assigned Concepcion and San Antonio to explore the strait, but the latter, commanded by Gómez, deserted and returned to Spain on 20 November. On 28 November the three remaining ships entered the South Pacific. Magellan named the waters the Mar Pacifico (Pacific Ocean) because of its apparent stillness.[19] Magellan and his crew were the first Europeans to reach Tierra del Fuego just east of the Pacific side of the strait.

Voyage of Circumnavigation: Funding and Preparation

Background: Spanish search for a westward route to Asia

The aim of Christopher Columbus' 1492–1503 voyages to the West had been to reach the Indies and to establish direct commercial relations between Spain and the Asian kingdoms. The Spanish soon realized that the lands of the Americas were not a part of Asia, but a new continent. The 1494 Treaty of Tordesillas reserved for Portugal the eastern routes that went around Africa, and Vasco da Gama and the Portuguese arrived in India in 1498. It became urgent for Spain to find a new commercial route to Asia, and after the Junta de Toro conference of 1505, the Spanish Crown set out to discover a route to the west. Spanish explorer Vasco Núñez de Balboa reached the Pacific Ocean in 1513 after crossing the Isthmus of Panama, and Juan Díaz de Solís died in Río de la Plata in 1516 while exploring South America in the service of Spain.

 Funding and preparation

In October 1517 in Seville, Magellan contacted Juan de Aranda, Factor of the Casa de Contratación. Then, following the arrival of his partner, Rui Faleiro, and with the support of Aranda, they presented their project to the Spanish king, Charles I, future Holy Roman Emperor Charles V. Magellan's project was particularly interesting, since it would open the "spice route" without damaging relations with the neighbouring Portuguese. The idea was in tune with the times. On 22 March 1518 the king named Magellan and Faleiro captains so that they could travel in search of the Spice Islands in July. He raised them to the rank of Commander of the Order of Santiago. The king granted them:

•    Monopoly of the discovered route for a period of ten years.
•    Their appointment as governors of the lands and islands found, with 5% of the resulting net gains.
•    A fifth of the gains of the travel.
•    The right to levy one thousand ducats on upcoming trips, paying only 5% on the remainder.
•    Granting of an island for each one, apart from the six richest, from which they would receive a fifteenth.

The expedition was funded largely by the Spanish Crown and provided with ships carrying supplies for two years of travel. Expert cartographer Jorge Reinel and Diogo Ribeiro, a Portuguese who had started working for Charles V in 1518 as a cartographer at the Casa de Contratación, took part in the development of the maps to be used in the travel. Several problems arose during the preparation of the trip, including lack of money, the king of Portugal trying to stop them, Magellan and other Portuguese incurring suspicion from the Spanish and the difficult nature of Faleiro. Finally, thanks to the tenacity of Magellan, the expedition was ready. Through the bishop Juan Rodríguez de Fonseca they obtained the participation of merchant Christopher de Haro, who provided a quarter of the funds and goods to barter.

ANCIENT NAVIGATORS: FERDINAND MAGELLAN ( 1480-1521)

A Portuguese nobleman, Ferdinand Magellan belonged to the romantic era of sea exploration characterized by Columbus and Vasco a Gama.

History books tell of his navigational prowess, ambition and courage in battle, describing his circumnavigation of the world as “the greatest”

single human achievement on the seas.

 In 1519 Magellan, under Spanish patronage, led an expedition of five ships to seek a westward passage to the Moluccas Islands. He discovered the Strait of Magellan (at the southern tip of South America) and gave the name "Pacific" to the Pacific Ocean based on its supposed calmness.

It was also a brutal three-year voyage that cost Magellan four ships 237 crew, and his own life. On route he killed several of his captains for mutiny and burned the villages of natives refusing to be Christianized.

His own down fall came in the Philippines while attacking a village that had failed to provide him with provisions.

Ancient Chart Of The Straits Of Magellan

Enlarged From The Chart Published At Madrid in 1769, by Don Juan de la Cruz Cano y Olmedilla of the Royal Academy of St. Fernando and Improved from the Observations and Surveys of Captns. Byron, Wallis and Carteret compared with those of Monsr. De Bougainville. (with) A Chart of Magellania with Falkland's Islands. London. Printed for R. Sayer and J. Bennett ... 1st July 1775. 

Secrets of Ancient Navigators: Chart and compass

 By Peter Tyson

The chart and the compass were two early technological breakthroughs that benefited seafarers. Photo credit: © DNY59/iStockphoto.com

Charts have aided mariners ever since the Alexandrian astronomer Ptolemy created the first world atlas in the second century A.D. The redoubtable Ptolemy even plotted latitude and longitude lines on his atlas's 27 maps, though the farther one got from the known world centered on the Mediterranean, the dangerously less reliable they became. Even before Ptolemy, there were sailing directions—the Greeks called them periplus or "circumnavigation"—that were compiled from information collected from sailors far and wide. One of these, The Periplus of the Erythraean Sea, a document written in the first century by a Greek merchant living in Alexandria, described trading routes as far east as India. By the 10th century, Italian-made portolans supplied detailed directions, distances, depths, and coastal descriptions, and by the 13th century, sea maps with scale and bearings began to appear.

The greatest advance in navigation came with the compass. The Chinese apparently knew about the powers of magnetism as early as the third millennium B.C., when, historians tell us, one army defeated another after the battlefield had become enveloped in dense fog by using a device known as a "point-south carriage." This was a standard carriage for carrying royalty with a small, rotating figure mounted on the front, which by magnetism always pointed south. (The Chinese chose to have the arrow point south rather than north.)

But no one seems to have manipulated the lodestone for sea navigation until early in the present millennium. The first mention of the compass in the West comes from the Englishman Alexander Neckham, who wrote in 1187 that "sailors use a magnetic needle which swings on a point and shows the direction of the north when the weather is overcast." Despite its usefulness, the compass took a long time to come into wide use, as many seamen thought it operated by black magic. (Hence the invention of the binnacle, in which sea captains could hide their recondite instrument from the suspicious eyes of the crew.) In the meantime, sailors relied on natural forces they could readily comprehend.

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Strait of Magellan: Incorporation into Chile

One of the most elegant and detailed charts of southern South America produced in the seventeenth century. The map continues the now archaic, headland view of Cape Horn but offers a much fuller picture of the west coast of Chile, identifying many capes and ports. 1675: Wit, Frederik de.

Chile took possession of the Strait of Magellan on May 23, 1843. President Bulnes of Chile ordered this expedition after consulting the Chilean libertador Bernardo O'Higgins (1778-1842), who feared an occupation by Great Britain or France. The first Chilean settlement was Fuerte Bulnes, situated in a forested zone on the north side of the strait. Fuerte Bulnes was later abandoned, and in 1848 the city of Punta Arenas was founded farther north where the Magellanic forests meets the Patagonian plains. In Tierra del Fuego, across the strait from Punta Arenas, the village of Porvenir emerged during the Tierra del Fuego gold rush in the late 19th century.

Argentina effectively recognized Chilean sovereignty over the Strait of Magellan in the Boundary treaty of 1881 between Chile and Argentina. Argentina had previously claimed all of the strait, or at least the eastern third of it.

In 1840 the Pacific Steam Navigation Company was the first to use steamships for commercial traffic in the strait.

Until the Panama Canal opened in 1914, the Strait of Magellan was the main route for steamships traveling from the Atlantic Ocean to the Pacific. It was often considered the only safe way to move between the Atlantic and Pacific Oceans, as the Drake Passage separating Cape Horn (the southern tip of South America) from Antarctica is notorious for turbulent and unpredictable weather, and is frequented by icebergs and sea ice. Ships in the strait, protected by Tierra del Fuego to the south and the coast of continental South America to the north crossed with relative ease, and Punta Arenas became a primary refueling port providing coal for steam ships in transit. Sailing ships, however, due in part to variable winds and currents in the strait, generally preferred the Drake Passage, as they had more room to maneuver there.

Strait of Magellan: Discovery by Europeans

The Strait of Magellan (also called the Straits of Magellan ) is a navigable sea route immediately south of mainland South America and north of Tierra del Fuego. The strait is the most important natural passage between the Atlantic and Pacific oceans, but it is considered a difficult route to navigate because of the unpredictable winds and currents and the narrowness of the passage.

Ferdinand Magellan, a Portuguese sailor in the service of Charles I of Spain, became the first European to navigate the strait in 1520 during his global circumnavigation voyage.

On March 22, 1518, the expedition was organized in Valladolid, naming Magellan captain general of the fleet and governor of all the lands discovered, and establishing the privileges of Magellan and his business associate Ruy Falero. The fleet would become known as the "Armada de las Molucas" or "Fleet of the Moluccas". The expeditionary fleet of 5 ships set sail from Sanlúcar de Barrameda on September 20, 1519.

The five ships included La Trinidad (100 to 110 barrels) under the command of Magellan; La San Antonio (120 barrels) under the command of Juan de Cartageña; La Concepción (90 barrels) under the command of Gaspar de Quezada (Juan Sebastián Elcano served as boatswain); La Victoria (85 barrels) under the command of Luis de Mendoza; and La Santiago, under command of Juan Rodríguez Serrano.

Magellan's ships entered the strait on November 1, 1520, All Saints' Day, and it was initially called Estrecho de Todos los Santos (Strait of All Saints). Magellan's chronicler, Antonio Pigafetta, called it the Patagonian Strait, and others Victoria Strait, commemorating the first ship entering it.] Within seven years it was being called Estrecho de Magallanes in honor of Magellan. The Spanish Empire and the Captaincy General of Chile used it as the southern boundary of their territory. The first Spanish colony was established in 1584 by Pedro Sarmiento de Gamboa, who founded Nombre de Jesús and Rey Don Felipe on the northern shore of the strait. These towns suffered severe food shortages, and when the English navigator Sir Thomas Cavendish landed at the site of Rey Don Felipe in 1587, he found only ruins of the settlement. He renamed the place Port Famine. Other early explorers included Francis Drake. The strait was first carefully explored and thoroughly charted by Phillip Parker King, who commanded the British survey vessel HMS Adventure, and in consort with HMS Beagle spent five years surveying the complex coasts around the strait. This survey was presented at a meeting of the Royal Geographical Society in 1831.