Gakkel Ridge, ~10mm

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 ~ 10mm.

A new analysis of rocks thought to be at least 2.5 billion years old by researchers at the Smithsonian’s National Museum of Natural History helps clarify the chemical history of Earth’s mantle—the geologic layer beneath the planet’s crust. The study, published today in the journal Nature, centered on a group of rocks collected from the seafloor that possessed unusual geochemical properties.