How old is the arctic circle

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Subscribe Ethical Shop. A mythical place — land of the frozen ocean, the aurora borealis and the midnight sun — the Arctic has long fascinated humankind. It has brought both riches and disaster to those who have tried to dominate it, while its indigenous people have been marginalized and exploited. Help us produce more like this Patreon is a platform that enables us to offer more to our readership. X New Internationalist is a lifeline for activists, campaigners and readers who value independent journalism.

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Crisis, crash, crunch - the lowlights. A sorry saga since corporate globalization got going in A brief history of population. Includes a murky past. The Arctic, by contrast, is diametrically different in several respects. Here, land masses surround an ocean that is centred on the pole. In contrast to the Southern Ocean, the Arctic Ocean has a permanent sea-ice cover whose area varies with the seasons. It achieves its greatest extent at the end of winter and its smallest size at the end of summer, whereby scientists are observing a steady decrease in the extent of summer ice.

Since the beginning of satellite measurements in , the surface area of summer ice has shrunk by around three million square kilometres. This is an area about eight times the size of Germany. Because the continents of Europe, Asia and North America extend far into the Arctic region, the Arctic has been more successfully settled by plants, animals and people than the Antarctic. Historical evidence suggests that the first aboriginal people were hunting in the coastal regions of the Arctic Ocean 45, years ago.

Today more than four million people live within the Arctic polar region. Where does the Arctic begin, where the Antarctic? Seamen at that time used the constellations of the northern sky, primarily Ursa Major and Ursa Minor, to aid them with orientation during their voyages of discovery.

The two circles mark the geographic latitudes at which the sun does not set on the dates of the respective summer solstices. In the northern hemisphere the summer solstice usually falls on the 21st of June and in the southern hemisphere it is usually the 21st or 22nd of December. They are currently moving toward the geographic poles by around The Arctic Circle has never become established, however, as the definitive southern boundary of the Arctic region.

North of this imaginary line the long-term average temperature for the month of July lies below ten degrees Celsius. By this criterion the Arctic Ocean, Greenland, Svalbard, large parts of Iceland, and the northern coasts and islands of Russia, Canada and Alaska all belong to the Arctic realm. In Siberia and North America, on the other hand, cold Arctic air pushes the temperature boundary further to the south, so that regions such as the northeastern part of Labrador, the Hudson Bay, and a large portion of the Bering Sea are included as part of the Arctic 1.

On the Arctic Circle it does not set for 24 hours, and on the Antarctic Circle it does not rise for 24 hours. Another natural southern boundary sometimes used for the northern polar region is the Arctic tree line.

As the name suggests, the present-day climate conditions north of this line are so harsh that trees are no longer able to survive. In North America, for example, this transition zone is a relatively narrow strip. In northern Europe and Asia, however, it can be up to kilometres wide.

In some areas, however, it can be located as much as kilometres to the south of the temperature boundary. According to this definition, western Alaska and the Aleutians would also belong to the Arctic, and the Arctic region would have a total area of around 20 million square kilometres.

A third natural boundary can be delineated based on ocean currents. According to this definition, the Arctic waters begin at the point where cold, relatively low-saline surface-water masses from the Arctic Ocean meet warmer more saline waters from the Atlantic or Pacific Ocean at the sea surface.

In the area of the Canadian Arctic Archipelago, the island group between North America and Greenland, this convergence zone extends to 63 degrees north latitude. As it continues eastward, it turns to the north between Baffin Island and Greenland.

In the Fram Strait, the marine area between East Greenland and Svalbard, it is located as far as 80 degrees north, i. On the other side of the Arctic Ocean, in the Bering Sea, the definition of a convergence zone is somewhat more difficult, because here the water masses from the Pacific and Arctic Oceans mix extensively with each other instead of one flowing over the other.

On maps, therefore, this vague boundary line runs straight across the narrow Bering Strait. Besides these three boundaries to the Arctic, which are all characterized by natural features, other boundaries have been defined according to different delineating criteria.

On the North American continent they draw the line at 60 degrees latitude. The most generous definition of the Arctic is found in the Arctic Human Development Report AHDR , where political and statistical aspects were considered in defining the area, which is why the boundary, especially in Siberia, extends further to the south than any other. If, in special cases, other definitions of the Arctic region are necessary, this will be specifically pointed out.

In the southern hemisphere, the definition of the boundary is not as difficult. The fact that the continent of Antarctica is essentially an island and the presence of distinctive ocean currents allow a relatively clear delineation of the boundary of the southern polar region.

This is the encircling oceanic zone where cold, northward-flowing surface water from the Antarctic meets warmer southward-flowing water masses from the north. The cold, saline water sinks as a result of the density differences, and is diverted beneath the warmer water masses. The precise position of the convergence zone, however, varies somewhat depending on longitude, the weather and time of year, and can therefore shift regionally by as much as kilometres to the north or south.

This World Ocean Review will conform to the delineation of the Antarctic polar region established in by the Antarctic Treaty unless otherwise noted. Wandering continents The fact that both polar regions of the Earth are covered with ice at the same time is an exceptional situation in the 4. The German polar researcher Alfred Wegener was the first to scientifically postulate that the continents are moving.

According to his theory the outer shell of the Earth, the crust, with a thickness of up to 60 kilometres, broke apart into large plates around three to four billion years ago. The plates travel at speeds up to ten centimetres per year. In this way, new continental or ocean crust is formed at the fractures. Climate researchers consider continental drift to be one of the most influential factors in the history of ice formation in the polar regions.

After all, the relative positions of the continents and oceans determine the patterns of air and ocean currents, and thus the distribution of heat on the planet.

In the past, parts of both regions have been located in the opposite hemispheres. Antarctica — an ancient continent In order to understand the origins of the southern polar region, it is necessary to know that the Antarctic continent actually consists of two parts: One is the relatively large, solid landmass of East Antarctica, which is composed of continental crust up to 3.

The other is West Antarctica, which comprises four considerably smaller and thinner crustal blocks. These four crustal fragments even today are not firmly connected to one another. They are constantly drifting. The geographic position and remoteness of Antarctica are relatively recent phenomena from a geological perspective. At least twice, in fact, it has been located far from the South Pole at the centre of a supercontinent. The first time was around one billion years ago, when all of the continents united as a consequence of worldwide mountain building to form the supercontinent Rodinia.

Some reconstructions place it beside Australia or Mexico. Which scenario is correct is still being debated today. Approximately million years later, during the Ordovician geological period, the Antarctic Continental Plate again moved to the centre of a great continent. This time it formed the core area of the giant Gondwana continent. This time it was bounded by India and Australia to the west and South America to the south.

Extra Info A volcanic landscape hidden below the ice Gondwana existed for a period of more than million years. These initiated the movement of the Antarctic Plate toward the south, which became possible as all of the neighbouring continents slowly broke off. The land masses of India and Madagascar then slowly drifted away toward the north, centimetre by centimetre. Then, between 90 and 80 million years ago, as New Zealand separated from Antarctica, the crustal blocks of West Antarctica were reorganized.

Hot magma currents within the Earth began to lift the blocks along their border to East Antarctica. It is to kilometres wide, more than kilometres long, and is one of the largest continental trench fault systems on the Earth — comparable in size to the East African Rift Valley, which runs through Africa from the Red Sea to Mozambique. The Antarctic continent could someday break apart along this active fault zone, but currently the trench is only widening by two millimetres per year, which is equal to about one metre every years.

The formation of the West Antarctic Rift zone about 80 million years ago was not the last tectonic milestone in the drift history of the Antarctic Continental Plate. One occurred at the plate boundary between South America and the Antarctic Peninsula where the spreading increased significantly 50 million years ago. Around 41 million years ago the Drake Passage opened here, an oceanic strait that is about kilometres wide today and connects the Pacific and Atlantic Oceans.

At the North Pole, the sun rises on the spring equinox in March. Then it lingers in the sky — without setting — until September's autumn equinox comes along. Between those dates, the big old star reaches its highest point in the polar sky on the summer solstice every June.

On Jan. Textbooks like to say the Arctic is an ocean surrounded by continents, while the Antarctic is a continent surrounded by an ocean. Here's something you might not realize about the arrangement. All that seawater under the North Pole moderates the climate to some extent. Yet the South Pole doesn't have this luxury.

As a result, the average winter temperature down there is a wicked degrees Fahrenheit degrees Celsius. By comparison, the North Pole's mean winter temperature of degrees Fahrenheit degrees Celsius feels downright balmy. Just as there's an Arctic Circle, the Antarctic has a circle of its own.

This begins at around Unlike its northern counterpart, the Antarctic Circle doesn't have any permanent human settlements. Research stations don't count. Nothing lasts forever. Slowly but surely, Earth's axial tilt is changing — and with it, the Arctic Circle. Every 40, years or so, this crucial tilt shifts from an angle of Right now, we're in the middle of one such cycle.

While that's going on, the boundary line that defines the Arctic Circle retreats by about 46 to 49 feet 14 to 15 meters northward per year. Remember Grimsey Island, the Icelandic outcrop we mentioned?

Well, scientists project that the Arctic Circle will leave the island behind by about the year Locals are using a concrete ball weighing about 8. Year by year, the sphere has moved to keep pace with the Arctic's receding circle. Twilight comes in three categories : civil, nautical and astronomical twilight. Respectively, these occur when the sun's geometric midpoint is 6, 12 and 18 degrees below the horizon. Of the trio, astronomical twilight is by far the dimmest.