New research shows ancient microorganisms helped trigger large-scale volcanic events.

Banded iron formations, sedimentary rocks with striking layers of burnt orange, yellow, silver, brown, and blue-black hues, may have been the catalyst for some of Earth’s largest volcanic eruptions in history, according to a recent Rice University study.

These rocks are composed of iron oxides that sank to the bottom of the ocean years ago and solidified over time into dense layers. A recently published study, Nature Geology He suggests that these iron-rich layers may act as a bridge connecting ancient surface changes, such as the emergence of photosynthetic life, to planetary processes such as volcanism and plate tectonics.

In addition to connecting planetary processes often thought to be unrelated, the research could change scientists’ understanding of Earth’s early history and provide insight into processes that could create habitable exoplanets far from our solar system.

“These rocks tell – literally – how the planetary environment has changed,” said Duncan Keller, lead author of the study and a postdoctoral fellow in Rice’s Division of Earth, Environmental and Planetary Sciences. “They embody changes in the chemical composition of the atmosphere and ocean.”

Duncan Keller is a postdoctoral fellow in Rice’s Division of Earth, Environmental and Planetary Sciences and lead author of the study published in Nature Geoscience. Credit: Jeff Fitlow/Rice University

Banded iron formations are chemical deposits that fall directly from old seawater rich in dissolved iron. The metabolic actions of microorganisms, including photosynthesis, are believed to contribute to the precipitation of minerals that form layer upon layer with silicon (microcrystalline silicon dioxide) over time. The largest deposits were formed about 2.5 billion years ago as a result of the accumulation of oxygen in the Earth’s atmosphere.

“These rocks were formed in ancient oceans, and we know that these oceans were later closed laterally by plate tectonic processes,” Keller said.

Although the mantle is solid, it flows like a liquid at approximately the rate of nail growth. Tectonic plates – continental-sized regions of the earth’s crust and upper mantle – are in constant motion, mainly due to thermal convection currents in the mantle. Earth’s tectonic processes control the life cycles of the oceans.

“As the Pacific Ocean closes today — sinking under Japan and South America — ancient ocean basins were tectonically destroyed,” he said. “These rocks were either pushed into the continents and preserved – and we see some preserved, which is where we look today – or they sank into the mantle.”

“We looked at the depositional age of banded iron formations and the age of large basalt eruptions, called large magmatic zones, and found a correlation,” Keller said. Said. “Many eruptive events—so massive that 10 or 15 of the largest could have been enough to animate the entire planet—had banded iron deposition at intervals of about 241 million years plus or minus 15 million years. This is a strong correlation with a logical mechanism.”

The study found that there is a time lag for banded iron formations to first pull deep into the lower mantle and then affect the heat flow to push the smoke thousands of kilometers above the Earth’s surface.

Trying to track down the banded iron formations, Keller crossed disciplinary boundaries and came across unexpected ideas. Source