Geologists have discovered in Greenland evidence for ancient life in rocks that are 3.7 billion years old. The find, if confirmed, would make these fossils the oldest on Earth and may change scientific understanding of the origins of life.

Experts are likely to debate whether the structures described in the new report were formed biologically or through natural processes. If biological, the great age of the fossils complicates the task of reconstructing the evolution of life from the chemicals naturally present on the early Earth. It leaves comparatively little time for evolution to have occurred and puts the process close to a time when Earth was being bombarded by destructive asteroids.

The fossils were discovered four years ago but not publicized while the geologists, a team led by Allen P. Nutman of the University of Wollongong in Australia, checked out their find.

“Of course one felt very excited, but we’re not the rushing types and we took our time,” Dr. Nutman said. “We kept it secret because we wanted to present it in the most robust way we could manage.”