EAGER: A Novel Approach to Study Earth's Oldest Environments and Biosphere: Tidal, Shelf, and Deep Ocean Habitats in the >3.7 Ga Isua Greenstone Belt, Greenland
Nora Noffke, Old Dominion University EAR-1232499
The Isua Greenstone Belt (IGB), Greenland, comprises the oldest, >3.7 Ga sediments preserved in Earth history. Until now the firm dogma is that all IGB rocks would be highly metamorphosed and therefore information on Earth's oldest paleoenvironment and the origin of life would be erased or so strongly masked that no firm conclusions can be drawn. This project allows analyses demonstrating the IGB constitutes a valuable archive on Earth's deepest time. Linda Hinnov's newly developed methods allow the PIs to reveal this unique information by analyzing bedding characters in shallow-marine deposits. The results will allow the understanding of the Earth-Moon constellation 3.7 Ga ago, the number of days per year, and possibly seasonality.
The project conducts research on some of the oldest sedimentary rocks from the 3.7 Ga (billion years) Isua Greenstone Belt, Greenland. The rocks are sedimentary and experienced a metamorphic overprint by temperature and pressure. Metamorphosis is caused by tectonic movement of rocks. However, the original rock beds are still preserved and can be examined from a sedimentologist's point of view. A rock that displays fine lamination (thin layers of rock) caught our attention, because such a layering is typical for coastal deposits in the ocean. What does such a marine rock tell us about Earth 3 billion years ago? The rock is a Banded iron Formation (BIF). This is a rock commonly composed of silica ("glass") and iron minerals. BIF is one of the most important iron ore deposits on Earth, where most iron is gained from. Our latest work examined the petrography of the BIF and determined that the content is silica alternating with grunerite (a carbonate mineral - now overprint by pressure and temperature due to tectonics). The presence of carbonate suggests that the original iron oxide mineral was siderite. In summary this BIF has a very simple mineralogy. A recent experiment showed that this mineralogy can form within minutes to hours (photochemically). Siderite and silica could have precipitated out of the water column. This allows us to explain the deposition of the rock in a coastal area more then 3 billion years ago. Interestingly, we can decipher a tidal rythm in the layers. This allows conclusions on the ancient Earth-Moon system at this early time period.
