Sunday, 20 November 2011

New Research Gives Insight Into The Evolution Of The Continent Of Antarctica

Antarctica is the fourth largest continent on Earth. It is often thought of as a barren, glacial continent, almost entirely devoid of life. Yet this could not be further from the truth as the ice sheets are full of micro-organisms. There are many thousands of migratory species, mainly birds, marine mammals such as the narwhal, and finally perennial, highly specialised creatures such as the penguins or various species of seal.

This was established when explorers began to survey the continent. What remained far more of a mystery was what lay beneath the ice sheets. Ice cores revealed that the frozen layer was incredibly thick. Yet exact depths were unknown. However, as technology such as radar became more advanced, the secrets of this sub-glacial world were slowly revealed. The first surprising data was collected during a Russian polar expedition in 1958.

It was thought originally that the base of the continent was a vast, flat, featureless expanse of frozen rock. The expedition found that it was actually covered in vast pinnacles, depressions and chasms. Some of these became well known such as Lake Vostok, the largest known sub-glacial body of water which has remained undisturbed for 25 million years, and is one of the last pure environments on Earth. Various teams have since returned to the frozen continent to study the hidden landscape under the ice.

The most recent study was conducted in 2008 to 2009 by a team led by Dr Fausto Ferraccioli from the British Antarctic Survey. Using aircraft, they passed back and forth over the continent, using an ice penetrating radar to build up a computer map of the underlying surface. The focus of their research was a vast mountain system called the Gamburtsev Range, which lies at the centre of Antarctica. These mountains are the same size as the European Alps.

A computer model of the continental composition around the Gamburtsev Mountain Range 
They were first discovered on the Russian expedition of 1958 and were long thought to be important. To find out how significant, the history of these mountains needed to be unravelled. Yet this was immensely difficult due to the 4000 metre thick ice sheets. Using a combination of airborne geophysics as well as seismological, gravitational and magnetic analysis to build up a model of the region, from the ice sheets, all the way down to the bedrock beneath the mountains, scientists were able to peal away the various layers and reveal the story of the Gamburtsev Range through time.
Models of the expansion of the Antarctic ice sheets
around the Gamburtsevs around 35 million years ago

The story begins a billion years ago during the Proterozoic eon. The ancient cratonic bedrock was fast becoming a part of the ancient super continent of Rhodinia. This pushed up a mountain range which were the precursors to the Gamburtsevs. Over hundreds of millions of years due to wind, ice and rain, this was eroded, leaving no trace.

Usually the bedrock of ancient mountains are eroded away also. However the compression of the rock during the assembly of Rhodinia, made it extremely hard wearing. So today, the Gamburtsevs are one of the few mountain ranges with an original geological root.

250 to 100 million years ago, the rifting of Pangaea created the modern day Gamburtsev Range. The events are rather ironic as the original mountains were destroyed in the formation of the ancient super continent, Rhodinia. Yet it took the destruction of another ancient super continent, Pangaea, to resurrect them.

The final chapter in this lengthy story came around 35 million years ago. At this time in prehistory, the continents were taking on their modern shape. Antarctica drifted south, occupying the cold polar ocean. The mountains were entombed in ice and became the nucleation point for what are today the Antarctic ice sheets. Dr Ferraccioli believes that the Gamburtsevs could reveal yet more secrets.

Drilling for samples of rock that may contain the most ancient ice in the world will allow scientists to accurately reconstruct the climate of the past million years. Such samples may be 200,000 years older than the oldest known ice today. 'Surveying these mountains was an incredible challenge, but we succeeded and it's produced a fascinating story,' Dr Fausto Ferraccioli stated in a press conference with the BBC. He hopes that future funding will enable the collection of further samples.