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In the Fact File section we bring you a new collection of quick facts each week. (Click on the links below for more facts)

 
 

2961/ On Easter Sunday, March 27th, 1513, Juan Ponce de Leon sailed from the Bahama island of San Salvador with three ships. He set out to discover a spring said trestore "age'd men to youths" that was to be found on the island of Bimini. He did discover a "spring" of sorts - a swift-flowing ocean river called the Florida Current, part of the Gulf Stream system of currents, which swept his ships far off course.

2962/ Continental basement rocks are "granitic"; they contain a high proportion of silica and aluminium. The seafloor crust is "basaltic"; it contains less silica and a high proportion of iron. Continents are therefore lighter than the ocean floors - like inebergs trapped in sea ice.

2963/ This accounts for the average 5km (3 miles) by which the continents are elevated above the seafloors. Since water always gravitates to the lowest point on any surface, it also accounts for the location of the oceans.

2964/ The Earth's north magnetic pole was discovered in 1831.

2965/ After its first discovery, the magnetic pole was rediscovered in 1903. It had moved a considerable distance. Todays magnetic polar region is nearly 800km (500 miles) NNW of its 1831 position. Such movement, during a relatively short period of time, may be a prelude to a complete reversal of the Earth's magnetic field.

2966/ The Earth's magnetic field has switched irregularly from north to south and back again innumerable times in the geological past in response to changing dynamo currents in the magnetic molten core of the Earth's core. The last reversal (from south to north) occurred about 700,000 years ago.

2967/ Ellesmere Island in the Canadian High Arctic is separated from Greenland by Nares strait. The narrow strait is over 480 km (300 miles) long and at its narrowest point only 25km (15 miles) wide. This is the site of an ancient suture between Greenland and North America.

2968/ It was many years before the proof of seafloor spreading and relative continental movement was broadly accepted by the geoscience community; the proof was in place by 1965, but the theory of plate tectonics that evolved from these discoveries was not embraced until the early 1970s.

2969/ The shape of the Earth is called the geoid. It is oblate - flatter at the Poles than at the Equator. But it changes as the planet resonates during its spin and responds to gravitational forces. Also it is either depressed or uplifted by the varying weight of ice on land or the distribution of shallow seas and oceans.

2970/ The Earth's core consists of two intimately related spheres. The outer core is a white hot semi liquid. It is composed mainly of iron; other elements include nickel and sulphur. It is about 2,250 km (1,400 miles) thick.

2971/ The inner core is a solid sphere of iron-nickel alloy with a radius of almost 1,600 km (1000 miles).

2972/ The mass of the Earth's core (31 percent) combined with the mass of the mantle and the asthenosphere (68.3%) make up 99.3 percent of the Earth's mass.

2973/ This leaves only 0.7 percent to account for the entire weight of the Earth's lithosphere - the thin rind of crust that includes the continental masses and supports the oceans.

2974/ The oldest known animal fossils on Earth are called "Ediacara" after a locality in Australia where they were first discovered.

2975/ The oldest known amphibians include Ichthyostega, a carniverous creature that could open its jaws wide enough to attack, kill, and feed off large victims - including other Ichthyostega.

2976/ According to the fossil record, land plants first appeared around 420 million years ago.

2977/ In Greek mythology Tethys was a sea goddess, who with her brother Iapetus - of Iapetus and Avalonia - was descended from Gaea, mother of the Earth.

2978/ Between 255 and 250 million years ago more than half the species of animals on Earth, including 75-95 percent of marine species, were permanently extinguished. This mass extinction is the greatest such event found in the fossil record.

2979/ Death Valley is one of the hottest desert regions on Earth: the highest recorded temperature there is 57.1 centigrade (134 F) in the shade.

2980/ Protoctista (minute life forms) are truly the artisans of the geological world, for they make (with their skeletal remains) over a billion tons of carbonate rock a year. They also make oil - in Cretaceous times, over a period of 30 million years, they produced perhaps 70 percent of the presently known global reserves of oil.

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