image: Orbulina universa, a planktonic foraminifera that evolved about 13 million years ago, was captured by scuba divers from surface waters off Santa Catalina Island, California. Photosynthetic dinoflagellate symbionts inhabit the calcite spines that radiate outwards from a central spherical shell composed of calcite (diameter ~0.5 mm). Following a four-week life cycle, the shells of these protists sink to the sea floor where they become part of the microfossil assemblage in deep-sea sediments. The geochemical compositions of such shells are used to reconstruct past ocean changes; for example, lithium isotope variations. This image relates to a paper that appeared in the Jan. 26, 2012, issue of Science Express, published by AAAS. The paper, by Sambuddha Misra at Florida State University in Tallahassee, Fla., and colleagues, was titled, “Lithium Isotope History of Cenozoic Seawater: Changes in Silicate Weathering and Reverse Weathering.” view more
Credit: [Image courtesy of Dr. Howard J. Spero, University of California, Davis]