When it comes to fossils, size doesn't matter; you can learn a lot even from really, really small ones. Among the tiniest fossils on Earth are single-celled, shelled marine organisms called foraminifera, which go back about 650 million years and are only about the size of the period at the end of this sentence. Scientists use foram fossils to analyze how Earth's climate has changed over time. "They're very sensitive indicators of environmental change," Neil Landman, curator in the Division of Palentology at the American Museum of Natural History, says in the latest episode of the museum's Shelf Life series.

"One way in which foraminifera can tell us something is by chemical analysis of the shells," research associate Ellen Thomas says. "You can look at the isotopic composition of the oxygen and the carbon and trace element concentrations in the shell. That means that we can say things about direct temperature of the past."

This analysis can tell scientists all kinds of things, from the size of the polar ice caps at the time the foram was fossilized to how much photosynthesis was happening in the ocean—and, therefore, the levels of carbon dioxide in the atmosphere. "If you look at reconstructions of climate ... in Wikipedia, for instance, then you'll see wiggly lines that tell you something about the climate of, say, the last 70 to 100 million years or so," Thomas says. "Those wiggly lines are all derived from from the analysis of foraminifera."

Back in the mid-20th century, Landman says, "the American Museum was the focus of foram study ... we have a very important collection here." Thanks to a grant from the National Science Foundation, the museum is rehousing the specimen slides and creating a digital catalog of the organisms, complete with photographs and 50 3D CT scans. "Forams are so cool because they're such tiny objects, yet they have so many complex features," says Shaun Mahmood, one of the interns working on the project. The CT scans show that "something the size of a grain of rice suddenly has 100 chambers that you didn't even know where there." Scientists can use those models to take measurements and even 3D print them—much, much bigger than the real creatures—to study. 

The project is important, Thomas says, because scientists "can use Earth's history and foraminifera in Earth's history to learn how life on Earth reacted to those events in the past and to help to predict how we are dealing with the future."