Which organism is a microscopic plankton with a silica shell, often used in paleoceanography?

• A. Pteropod
• B. Radiolarian
• C. Sand
• D. Nodule

Answer: (B)

Radiolarians are microscopic plankton that build intricate silica skeletons. Their silica tests fossilize well and accumulate as a siliceous ooze in deep-sea sediments, creating rich microfossil records. In paleoceanography, these shells serve as valuable proxies because the species present and their relative abundances change with water temperature, nutrient conditions, and ocean circulation. By examining radiolarian assemblages in sediment cores, scientists can reconstruct past ocean climates and even estimate the ages of deposition through biostratigraphy. Pteropods have calcium carbonate shells, not silica; and sand or a nodule are inorganic particles, not living microfossils, so they don’t fit the description.