Visually striking layers of burnt orange, yellow, silver, brown and blue-black colors are characteristic of banded iron formations, sedimentary rocks that may have produced some of the largest volcanic eruptions in Earth’s history, according to a new study from Rice University.

The rocks contain iron oxides that form dense layers that long ago settled to the bottom of the oceans and eventually turned into stone. A study published this week Nature Geology, He suggests that iron-rich layers may link ancient changes on the Earth’s surface, such as the emergence of photosynthetic life, to planetary processes such as volcanism and plate tectonics.

In addition to linking planetary processes that are generally thought to be unrelated, the study could change scientists’ understanding of Earth’s early history and provide insight into processes that may have created 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.”

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, that’s where what we look at today came from – or they were trapped in the mantle.”