The formation of the Earth, as we understand it today, was shaped by numerous and powerful volcanic events. The trigger point of these just might have related to something unexpected: microbial activity. Researchers have been examining iron-rich rocks and they have unlocked a remarkable new insight into Earth’s planetary history
The research from Rice University suggests ancient microorganisms (archaea) were the causative agent for massive volcanic events. This has arisen from studies into the banded iron formations – sedimentary rocks – connected with some of the largest volcanic eruptions in Earth’s history.
These rocks contain iron oxides, and they sank to the bottom of oceans billions of years ago, forming dense layers that eventually turned to stone. The researchers speculate that the iron-rich layers connect ancient changes at Earth’s surface, such as the emergence of photosynthetic life, to volcanism and plate tectonics.
Banded iron formations are chemical sediments precipitated directly from ancient seawater rich in dissolved iron. Metabolic actions of microorganisms, such as photosynthesis, facilitated the precipitation of the minerals, which formed layer upon layer over time along with chert (microcrystalline silicon dioxide).
Due to the high iron content, banded iron formations are denser than the mantle. The researchers believe subducted chunks of the formations sank down and settled in the lowest region of the mantle near the top of Earth’s core. Here, under immense temperature and pressure, the rocks would have undergone profound changes as their minerals took on different structures.
Under these conditions, iron oxides become highly thermally and electrically conductive. The regions enriched in subducted iron formations might have aided the formation of mantle plumes. These rising conduits of hot rock can produce enormous volcanoes like the ones that formed the Hawaiian Islands.
The researchers have formed this view after studying depositional ages of banded iron formations and the ages of large basaltic eruption events and noted a correlation, since each event appears to have been preceded by banded iron formation deposition.
In terms of where microbes come in, in the Earth’s early oceans microorganisms chemically changed the surface environments. This created an enormous outpouring of lava somewhere else on Earth 250 million years later.
The findings form part of the CLEVER Planets initiative: Cycles of Life-Essential Volatile Elements in Rocky Planets program, which is an interdisciplinary, multi-institutional group of scientists looking at how volatile elements that are important for biology — carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur — behave in planets, at how planets acquire these elements and the role they play in potentially making planets habitable.
This means what has happened on Earth could provide the basis for seeking out the potential for life on other planets.
The research appears in the journal Nature Geoscience, titled “Links between large igneous province volcanism and subducted iron formations.”
