Evolving

How Antarctica was formed

          Until about 160 million years ago, Antarctica was part of a much larger continent called Gondwana. It was in fact a supercontinent which also included India, Africa, South America, New Zealand and Australia. About 560 million years ago, Antarctica was north of the Equator. Evidence for this has been supported by specimens found of tropical plant fossils. Over about 100 million years, the continents broke up and slowly moved into their present positions. Scientists have been able to support their theories for these great continental movements through plate tectonics, which shows how the earth's crust and plates move and fit together like a jigjaw puzzle. These plates, however, move continually. This is usually very subtle and over extremely long periods in time. Where the plates have rubbed together they have formed mountain ranges, where they move apart they cause earthquakes and where cracks open up to the molten lava below the earth's crust, you get volcanoes. We therefore know about Gondwana's existence as the land masses fit so snugly together but also, more importantly, because similar rocks and fossils have been found in each continent. Australia separated from Antarctica about 56 million years ago and drifted northwards to its present position.The site of this Antarctic and Southern Ocean Centre sits on an old quarry which is comprised of Antarctic dolerite rock! If you dug into that Antarctic rock (about 40 million years deep), you would find beech tree fossils, like the beech trees growing in Tasmania today.

          Under the plate tectonic theory, the Antarctic continent was formed from the break-up of the supercontinent Gondwana. Antarctica lies on a single lithospheric "plate". Most of the Antarctic geologic record lies hidden beneath vast regions of snow and ice, with rock outcrops making up only about 2% of the land surface The thick ice sheet, the extremely difficult working conditions, and the expense of expeditions have made the geology of Antarctica less known than that of any other continent. The Antarctic continent is the largest apparently earthquake free area of the world. Seismic observatories have measured tremors but these are commonly attributed to fracturing of the ice sheet, to calving of ice shelves and to volcanic activity. Seismic and gravity studies have also shown that the thickness of the Earth's crust beneath Antarctica is not uniform. Antarctica can be broadly divided into two parts. The crust thickens sharply along the Transantarctic Mountains, possibly a deep crustal fault system, between the thinner crust of West Antarctica and the much larger and thicker crust of East Antarctica which averages about 25 miles in thickness. The tallest mountain in Antarctica is Vinson Massif in the Ellsworth Mountains at 5,140 metres.

          Ninety eight percent of Antarctica is covered in ice. The remaining, uncovered 2% of Antarctica has a great deal to tell about how life on Earth developed and how the continents were formed. Fossils of trees which grew in Antarctica show that its climate was once much warmer and its vegetation was not unlike some present-day Tasmanian plants. Fossils found in the Transantarctic mountains by early explorers showed that Antarctica, Australia, New Zealand, Africa, South America and India were once part of a supercontinent called Gondwana. A massive (12 kilometre square) fossilised river bed shows where shoals of fish once swam during the Cretaceous Era, just before 70% of the world's species, (including the dinosaurs) were wiped out by a spectacular disaster some 65 million years ago. The prime suspect is thought to be a huge asteroid which struck the Earth near Mexico, blanketing the Earth in dust. Other Antarctic fossils show that between 3-4 million years ago a species of dolphin that swam in a sea not far from what is now Australia's Davis Station, suggesting that the sea must have been higher than it is today and the temperatures warmer.

          Geomorphology is the study of the shape of the earth. This includes the description of mountains, valleys, ocean basins and plains that compose the earth's surface. The geomorphology of Antarctica is different from the other continents because of the presence of the ice sheet which covers most of the land. The average elevation of Antarctica is 2,300 metres which makes it the highest continent (Australia has an average elevation of only 300 metres and North America is only 720 metres). The top of the ice cap forms a flat surface over 1,500 kilometres across known as the Polar Plateau. Many parts of the ice sheet are resting on land that is actually below sea level, so if you melted the Antarctic ice cap the area of the land left behind would only be about half of the size of present Antarctica. The Antarctic continent can be divided into two parts, east and west, which have different geological origins and a different basement expression. East Antarctica is geologically much older, dating back more than 3 billion years and forms a large continental shield. West Antarctica is much younger and is really a chain of separate islands; the two halves are separated by the Trans-Antarctic Mountains.

Terra Incognita Index

Ice sheets