New research from Rice University has revealed that banded iron formations, characterized by visually striking layers of burnt orange, yellow, silver, brown, and blue-tinged black, may have triggered some of the largest volcanic eruptions in Earth’s history. These sedimentary rocks contain iron oxides that settled at the bottom of ancient oceans, forming dense layers that eventually hardened into stone. The study, published in Nature Geoscience, suggests that the iron-rich layers could connect changes in Earth’s surface, such as the emergence of photosynthetic life, to planetary processes like volcanism and plate tectonics.
Banded iron formations are believed to have formed from chemical sediments precipitated from seawater rich in dissolved iron. Microorganisms, including those involved in photosynthesis, are thought to have played a role in facilitating the formation of these minerals, which accumulated layer by layer over time alongside chert (microcrystalline silicon dioxide). The largest deposits appeared as oxygen accumulated in Earth’s atmosphere approximately 2.5 billion years ago.
According to Duncan Keller, the lead author of the study, these rocks serve as a literal record of a changing planetary environment and provide insight into shifts in atmospheric and ocean chemistry. The ancient oceans where these rocks formed were later closed off by plate tectonic processes, which caused the ancient ocean basins to be destroyed. Some of these rocks were pushed up onto continents and preserved, while others were subducted into the mantle.
Keller’s curiosity was piqued by the high iron content of banded iron formations, leading him to speculate whether subducted portions of these formations sank deep into the mantle and settled near the top of Earth’s core. Under extreme temperature and pressure conditions, these rocks may have undergone significant changes, with their minerals adopting different structures. Some iron oxides, at such depths, exhibit highly conductive properties and can transfer heat as easily as metals, suggesting that these rocks could have transformed into extremely conductive lumps resembling hot plates.
The researchers propose that regions enriched in subducted iron formations may contribute to the formation of mantle plumes. Mantle plumes are rising columns of hot rock that originate from thermal anomalies in the lower mantle and can give rise to massive volcanic activity, similar to the volcanic activity responsible for the creation of the Hawaiian Islands.
By examining the ages of banded iron formations and large basaltic eruption events known as large igneous provinces, the study revealed a correlation between the two. The researchers found that many of the immense igneous events, potentially capable of resurfacing the entire planet, were preceded by banded iron formation deposition at intervals of approximately 241 million years. This correlation suggests a plausible mechanism connecting the deep sinking of banded iron formations in the lower mantle to the subsequent formation of mantle plumes thousands of kilometers above the Earth’s surface.
The study highlights the interconnectedness of various Earth processes and challenges previous assumptions about Earth’s early history. It also offers valuable insights into processes that could occur on habitable exoplanets outside our solar system.
Duncan Keller hopes that this research will inspire further collaboration and investigation among scientists in different fields, fostering renewed discussions about the interconnectedness of different components of the Earth system. The study is part of the CLEVER Planets program, which aims to understand the behavior of volatile elements crucial for life, such as carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, in rocky planets.
Source: Rice University