Saturday, 12 October 2013

Updating The Story Of Oxygen

Antoine Lavoisier was the first to identify oxygen as a new element.
In its liquid form, it possesses a beautiful blue colour
During the 18th century chemistry came of age. Yet an alchemic throwback was phlogiston, thought to be a corrosive and combustible element responsible for fire and explosions. Described as an odorless, colourless, and even weightless gas, nobody had managed to isolate it from air. As time progressed, however, some chemists smelt a rat.

The Father of Modern Chemistry, Antoine Lavoisier, whose execution at the hands of the French Revolutionaries has been noted as the single greatest loss to science in history, managed before his death, to dispel the phlogiston myth. Lavoisier demonstrated that the element responsible for combustion in air was oxygen.

Today we know its importance to the development of the Earth and life: affecting the fundamental biochemistry of all cells, the biochemical process of death, the source of evolutionary innovation, and the growth/shrinkage in animal and plant diversity in response to changes in atmospheric levels. Geological data shows that Oxygen rapidly increased in concentration around 2.3 billion years ago.

Some of the rocks used in the study. The red line represents the ancient soil
horizon. Its red colour comes from a high concentration of oxidized minerals
Yet exciting new geochemical evidence shows that Earth's atmosphere contained an important amount of oxygen at least 700 million years before previous, accepted calculations. By studying prehistoric soils from South Africa, researchers led by Sean Crowe from the University of British Columbia, have identified an atmospheric oxygen signature, dating back to around 3 billion years ago.

It had long been thought that photosynthetic cyanobacteria, which produce oxygen, evolved at least three billion years ago, if not earlier. Yet there is not a truly significant rise in the level of atmospheric oxygen until 2.3 billion years ago during the Great Oxidation Event. It had been assumed that this was due to a drop in volcanic activity.

Photosynthetic cyanobacteria were the first great source of oxygen on Earth.
This study suggests that they evolved at least 3 billion years ago
Yet for oxygen to have been present in the atmosphere 3 billion years ago, there must have been a powerful source of the gas. 'We've always known that oxygen production by photosynthesis led to the eventual oxygenation of the atmosphere and the evolution of aerobic life,' said Professor Crowe.

'These findings imply that it took a very long time for geological and biological processes to conspire and produce the oxygen-rich atmosphere we now enjoy,' added Lasse Døssing, from the University of Copenhagen.

Our understanding of the events of the Precambrian are intimately connected with the story of oxygen. While Lavoisier could not have appreciated the true significance of his discovery and what it would lead to, his isolation of oxygen proved to be one of the most important contributions to science.