In 2008, scientists studying modern deep-sea protists used their observations to extrapolate information about ancient protists. In particular, they studied the profusion of macroscopic groovelike traces in rock called trace fossils—the remnants of trails made by ancient organisms. Comparing 1.8 billion-year-old protist trace fossils to the trails of living, grape-sized protists called Gromia sphaerica, the scientists found a great similarity, concluding that many of these organisms were around in profusion much earlier than previously thought.

The study of ancient protists is important to scientists trying to understand life on early Earth. This is because the early protists—especially the protozoa (single-celled organisms that live mostly in water)—are thought to have been the first complex organisms on Earth. It is thought that they evolved from primitive cells 2 to 1.5 billion years ago, and those early organisms may have been a cross between plants and animals. They may have also had symbiotic relationships with bacterialike organisms, eventually leading to multicelled organisms. All of this is speculation, mainly because the fossil record of such creatures is so sparse—thanks to the organism’s size (they are difficult to find in rock) and the fact that it probably decays quickly, leaving no trace.