Ancient microorganisms associated with massive volcanic events

May 26. (EUROPE PRESS) –

Iron-rich layers under the ocean floor could connect ancient changes on Earth’s surface, as the emergence of photosynthetic lifewith volcanism and plate tectonics.

Visually striking strata of burnt orange, yellow, silver, brown, and blue-tinged black are characteristic of these banded iron formations, according to new research from Rice University. published in Nature Geoscience.

“These rocks literally tell the story of a changing planetary environment,” he said. it’s a statement Duncan Keller, lead author of the study and a postdoctoral researcher in Rice’s Department of Earth, Planetary and Environmental Sciences. “They embody a change in atmospheric and ocean chemistry.”

Banded iron formations are chemical sediments precipitated directly from ancient seawater rich in dissolved iron. The metabolic actions of microorganisms, including photosynthesis, are thought to have facilitated the precipitation of minerals., which formed layer upon layer over time along with flint (microcrystalline silicon dioxide). The largest deposits formed when oxygen accumulated in Earth’s atmosphere about 2.5 billion years ago.

“These rocks formed in ancient oceans, and we know that those oceans were then laterally closed by plate tectonic processes,” Keller explained.

The coat, though solid, flows like a fluid at the same rate as fingernails grow. Plate tectonics, continent-sized sections of the crust and upper mantle, are in constant motion, largely as a result of thermal convection currents in the mantle. Tectonic processes on Earth control the life cycles of the oceans.

“Just like the Pacific Ocean is closing today, it’s sinking under Japan and South America, the ancient ocean basins were tectonically destroyed,” he said. “These rocks had to be pushed onto the continents and preserved, and we see some preserved, that’s where the ones we’re seeing today come from, or subducted into the mantle.”

Because of their high iron content, banded iron formations are denser than the mantle, causing Keller to wonder if subducted fragments of the formations sank to the bottom and settled in the lower region of the mantle. , near the top of the Earth’s core. There, under immense temperature and pressure, they would have undergone profound changes as their minerals acquired different structures.

“There is some very interesting work on the properties of iron oxides under those conditions,” Keller said. “They can become highly conductive thermally and electrically. Some of them transfer heat as easily as metals do. So it’s possible that, once in the lower mantle, these rocks become extremely conductive deposits like hot plates.”

Keller and his coworkers postulate that regions enriched in subducted iron formations could help form mantle plumes, risers of hot rock above thermal anomalies in the lower mantle. that can produce huge volcanoes like the ones that formed the Hawaiian Islands.

“Below Hawaii, the seismological data shows us a hot mantle upwelling conduit,” Keller said. “Imagine a hot spot on your stove burner. As the water in the pot boils, you’ll see more bubbles above a rising column of water in that area. The mantle feathers are kind of a giant version of that.”

“We looked at the depositional ages of banded iron formations and the ages of large basaltic eruption events called large igneous provinces, and found that there is a correlation,” Keller said. “Many of the igneous events, which were so massive that the largest 10 or 15 may have been enough to reemerge at the surface of the entire planet, were preceded by the deposition of banded iron formations at intervals of about 241 million years, more or less 15 million. It’s a strong correlation to a mechanism that makes sense.“.

The study showed that there was a plausible time period for the banded iron formations to first be drawn deep into the lower mantle and then influence the heat flux to propel a plume toward the Earth’s surface thousands of kilometers high. .

In his effort to trace the journey of iron band formations, Keller crossed disciplinary boundaries and stumbled upon unexpected insights.

“If what’s happening in the early oceans, after microorganisms chemically changed surface environments, ultimately creates a huge lava outpouring somewhere else on Earth 250 million years later, that means these processes are related and ‘talking’ to each otherKeller said. “It also means that related processes may have much larger length scales than expected. In order to infer this, we had to draw on data from many different fields in mineralogy, geochemistry, geophysics, and sedimentology.”