Foraminifera, or “forams” for short, are the tiny marine creatures that create little calcite shells, or tests, which drift down to the ocean floor once the animal inside has died. The tests have a distinctive shape, which varies from species to species; some look (under magnification) like beehives, others like braids or bubbles or clusters of grapes. Forams tend to be widely distributed and abundantly preserved, and this makes them extremely useful as index fossils: on the basis of which species of forams are found in a given layer of rock, an expert like Silva can tell the rock’s age.
