Scientists from the Smithsonian’s National Museum of Natural History have analyzed ancient rocks, estimated to be at least 2.5 billion years old, providing insights into Earth’s mantle history and challenging earlier theories about its geologic past. The study reveals that most of Earth’s mantle has maintained a stable oxidation state throughout geological time.
Researchers examined unique rocks collected from the seafloor with unusual geochemical properties, including high degrees of melting and low oxidization levels. They reasoned these rocks must have melted deep within the Earth during extremely hot conditions. The only known period in Earth’s history with such temperatures was between 2.5 and 4 billion years ago, during the Archean Eon.
These findings dispute earlier theories suggesting that Earth’s mantle became more oxidized over billions of years due to various mechanisms like a loss of gasses to space or subduction recycling. Instead, researchers argue that high temperatures during the Archean caused parts of the mantle to be less oxidized. Since then, Earth’s mantle has cooled, making it unable to produce rocks with extremely low oxidation levels anymore.
The team is now working to better understand the geochemical processes that shaped the Archean mantle by simulating high pressures and temperatures in the lab. The study was funded by the Smithsonian and the National Science Foundation.
Source: https://scitechdaily.com/2-5-billion-year-old-time-capsule-rocks-rewrite-history-new-study-challenges-mantle-oxidation-theory/