March 2, 2013
Mineral Contamination Reflects Historical Changes To Earth’s Geochemistry
redOrbit Staff & Wire Reports - Your Universe Online
A new study focusing on the mineral molybdenite could provide new insight into the way that various geological and biological processes have resulted in changes to the Earth´s chemistry over the years.
According to Robert Hazen of the Carnegie Institution for Science´s Geophysical Laboratory, molybdenite is a common ore mineral of a metallic element known as molybdenum. By analyzing samples of the substance obtained from various locations and various different eras, they were able to track historical chemical reactions with oxygen found in the environment.
The study is known as mineral evolution, and according to the researchers it is a new way to better understand our planet´s changing near-surface geochemistry. As they explain it, every chemical element has been present in the solar system from its very beginnings. Minerals, however, are a different story. They formed very slowly at first, with perhaps as few as 500 different chemical combinations coming together during the first billion years. It was only as time passed that different elements started to combine, resulting in new minerals.
One of those minerals was molybdenite, and it was selected by Hazen and his associates as the focus of their mineral evolution research. They analyzed more than 400 samples between the ages of 2.91 billion years to 6.3 million years and taken from 135 different locations throughout the world. The researchers were looking for traces of contamination from the element rhenium, which they explained could be used to track past chemical reactions with oxygen because it is sensitive to oxidation reactions.
Hazen´s team discovered that rhenium concentrations increased eight-fold over the past three billion years, leading them to believe that the finding demonstrates increasing near-surface oxidation conditions from the Archaen Eon (approximately 2.5 billion years ago) to the Phanerzoic Eon (less than 542 million years ago). That increase was the result of what is known as the Great Oxidation Event — a phenomenon during which oxygen-producing photosynthetic microbes caused the atmospheric levels of the element to skyrocket, according to the researchers.
Furthermore, “they found that the distribution of molybdenite deposits through time roughly correlates with five periods of supercontinent formation, the assemblies of Kenorland, Nuna, Rodinia, Pannotia, and Pangea,” the Carnegie Institution said in a statement Thursday. “This correlation supports previous findings from Hazen and his colleagues that mineral formation increases markedly during episodes of continental convergence and supercontinent assembly and that a dearth of mineral deposits form during periods of tectonic stability."
"Our work continues to demonstrate that a major driving force for mineral evolution is hydrothermal activity associated with colliding continents and the increasing oxygen content of the atmosphere caused by the rise of life on Earth," Hazen added. His team´s study has been published in the journal Earth and Planetary Science Letters (EPSL).