Geology


The Antarctic continent we know today has not always been located where it is now, nor has it always been so cold. The presence of coal (formed from ancient vegetation), and fossils of tropical plans and animals show that Antarctica was once considerably warmer, which means closer to the equator. Antarctica, as it appears today, has existed only for the past 60 million years. Somehow the continent drifted to its present position over the South Pole -- an idea first proposed in 1912, by the German scientist Alfred Wegner.















Gondwanaland

To picture the origins of the continent it is necessary to go back in time to the giant southern hemisphere land-mass known as Gondwanaland, which existed from 500 million years ago to 160 million years ago. At this time the eastern part of Antarctica formed the core of this "super continent" which also included Africa, South America, India, Australia and New Zealand. Evidence for this link up can be found in the similar geology of the southern parts of these continents, evidence which led Wegner to propose his Theory of Continental Drift.

It took time for the evidence to catch up with his theory, which was not accepted for 40 years. Now called "plate tectonics", it suggests that the continents move about on convection currents in the earth's molten interior. Over centuries and millennia, this can cause continents to collide and break up. Other portions of Gondwanaland -- the name comes from Gondwana, a province in India where fossil leaves lent evidence to Wegner's theory -- began to break up about 200 million years ago, each plate radiating out in separate directions to form the land masses we are familiar with today.


Fossil ammonite from the Antarctic Peninsula

By 60 million years ago, continental drift had begun to form of a deep ocean between the Antarctic and Australia. What is now known as Drake Passage, the sea route between Antarctica and South America, began to open. This led to the formation of the Antarctic Circumpolar Current some 28 million years ago, which isolated the continent from the warmer oceans of the world.

In response to this cooling 25 million years ago, all the forests, ferns, freshwater fish, amphibians and reptiles disappeared, and the Antarctic became covered with ice. Today, evidence of these once-common floral and faunal species appears only as fossils. Linking species still found today in Tasmania, New Zealand, and Terra del Fuego bear a strong resemblance to the Antarctic beech Nothafagus. Return


Greater and Lesser Antarctica

The Antarctic is divided into two main regions, East Antarctica or "Greater Antarctica" and West Antarctica or "Lesser Antarctica", which are quite different geologically from each other. Greater Antarctica consists of a stable shield of very ancient rocks (pre-Cambrian) older than 570 million years and mostly above sea-level. Some rocks have been dated as far back as 380 million years. West Antarctica would, if the ice were removed, be simply a string of islands. The two regions are separated by the Trans Antarctic Mountains. In most places, mountain peaks protrude above the icecap. But the remainder of the topography of the continent is largely hidden beneath the ice. Return


Oases


Only between two and four percent of the Antarctic is snow-free. The main such areas of Antarctica are the isolated tips of mountains (nunataks), the edges of the continent where the icesheet leaves exposed rock, and oases. Oases are large areas of ice-free land that look more akin to deserts of lower latitudes. They only occur in East Antarctica and the largest of these are the Dry Valleys of Victoria Land on the edge of the Ross Sea. The three main valleys and the Taylor, the Wright and the Victoria Valley were once filled with glaciers that have long since retreated. Other significant oases in Antarctica are the Bunger Hills, the Vestfold Hills, the Prince Charles Mountains and the Lasserman Hills.


Many of these lakes are extremely saline as a result of progressive evaporation. This high salinity creates an environment that most life forms cannot survive, although some phytoplankton and zooplankton have evolved mechanisms for coping with these extremes. Return


Mountains

Mountain ranges that rise above the icecap are further significant snow-free sites. The Antarctic has one of the longest mountain chains in the world, the Transantarctic Mountains that extend from the tip of the Antarctic Peninsula to Cape Adare, a distance of 3000 miles (4800 km). In many places the chain is mostly buried, but the exposed peaks often have steep snow free faces.

Antarctica is the highest continent, with an estimated average height of 2,300 meters (7500 ft). This compares with the next highest continent, Asia, which has an average height of about 900 meters and Australia's average of 340 meters. However, without its ice cover Antarctica would only rise about 450 meters above sea-level.

There are numerous other mountain ranges in the Antarctic, such as the Prince Charles Mountains, the Shackleton Range, the Edsel Ford Range, and the Pensacola Mountains. Most notable is the Sentinel Range, first discovered by Lincoln Ellsworth in 1935 on his epic transcontinental flight and considered part of a larger area of mountains that now bears his name. Mount Vinson, the highest point in Antarctica, is in the Sentinel, crowning the range at 16,067 feet.

Around the edges of East Antarctica there are numerous smaller snow free areas and islands where the bare rock occurs as a result of the effects of local topography and contortions of the icecap. These are where the main wildlife breeding colonies can be found, and are the most popular sites for permanent scientific stations. Return
Photography ©Jonathan Chester, Extreme Images© 1995 Terraquest. All Rights Reserved.