New Study Challenges Mantle Oxidation Theory

A thin slice of the ancient rocks collected from Gakkel Ridge near the North Pole, photographed under a microscope and seen under cross-polarized light. Field width ~ 14mm. Analyzing rocks in thin section helps geologists identify and characterize minerals within a rock. The analyses reveal information about the rock’s mineral composition, texture and history, such as how it formed and any subsequent changes it has undergone. Researchers use the identification and chemical composition of the minerals in these ancient rocks from Earth’s mantle to determine the conditions under which these rocks melted. Credit: E. Cottrell, Smithsonian

Smithsonian scientists conduct new research on ancient ‘time capsule’ rocks, dating back at least 2.5 billion years.

Researchers at the Smithsonian’s National Museum of Natural History have conducted a new analysis of rocks believed to be at least 2.5 billion years old, shedding light on the chemical history of Earth’s mantle, the layer beneath the planet’s crust. Their findings enhance our understanding of Earth’s earliest geologic processes and contribute to a long-standing scientific debate regarding the planet’s geologic history. Notably, the study provides evidence that the oxidation state of most of Earth’s mantle has remained stable over geological time, challenging previous assertions by other researchers about major transitions.

“This study tells us more about how this special place in which we live came to be the way it is, with its unique surface and interior that have allowed life and liquid water to exist,” said Elizabeth Cottrell, chair of the museum’s department of mineral sciences, curator of the National Rock Collection and co-author of the study. “It’s part of our story as humans because our origins all trace back to how Earth formed and how it has evolved.”

The study, published in the journal Nature, centered on a group of rocks collected from the seafloor that possessed unusual geochemical properties. Namely, the rocks show evidence of having melted to an extreme degree with very low levels of oxidation; oxidation is when an

An ancient rock dredged from the seafloor and studied by the research team. Credit: Tom Kleindinst