Saturday, 3 December 2011

A New Model For The Earth's Early Atmosphere

A polished surface of the oldest known zircon crystal on Earth
In 1953, the Russian biochemist Alexander Oparin discovered that organic molecules, vital to the creation of life, could not be created in an oxygenated atmosphere. His findings quickly defined the model which all scientists used when investigating the early atmosphere and its influences on the origins of life. Later experiments established other organic molecules such as methane and ammonia, alongside ambient molecules such as water and carbon dioxide.

Geochemical evidence seemed to support these theories. Yet a recent study of ancient zircon minerals, by scientists at the New York Centre for Astrobiology at Rensselaer Polytechnic Institute, suggests that the atmosphere of our young planet, just 500 million years after its creation, may have a rather different chemical composition than previously thought. Zircon minerals, composed of zirconium oxide, are some of the oldest known fragments of the Earth, with Australian samples giving a truly incredible date of 4.404 billion years old.

These crystalline milestones trap small amounts of the ambient compounds present during formation, allowing scientists to reconstruct the atmospheric conditions at different points in the Earth's history. The team led by Bruce Watson, Institute Professor for Science at Rensselaer, recreated conditions to study the way zircon crystals formed, providing an insight into the evolution of the Earth's atmosphere. They did this literally by making lava in the lab.

From this, they were able to create an oxidisation gauge by looking at trace compounds of the rare earth element Cerium. Cerium is a rather interesting element as it can bond with different amounts of oxygen to form two different oxides (Ce2O3) and (CeO2). They found a higher concentration of Ce2O3. They concluded that the early atmosphere contained a far higher level of oxygen than previously thought.

As there would be enough reactive elements within the atmosphere to combine with the oxygen to form compounds, the conditions set by Oparin for the formation of organic molecules is still satisfied. 'We can now say with some certainty that many scientists studying the origins of life on Earth simply picked the wrong atmosphere' said Watson. This study is likely to set the base line for future studies of the Earth's early atmosphere and the creation of life itself.