Microscopic, single-celled organisms called foraminifera have a fossil record that extends from today to more than 500 million years ago. Although each foram is just a single cell, they build complex shells around themselves from minerals in the seawater. These shells have accumulated in layers of sediment below the seafloor of the open ocean and in regions where the ocean once flooded the continents for millions of years. By examining the shell chemistry of these ancient forams, scientists can learn about Earth's climate long before humans ever walked the planet—and get insight into how climate changed in the past. Take a closer look at a few members of this fascinating life form.