NASA-supported scientists have resurrected an enzyme first used by organisms on Earth 3.2-billion years ago and, in the process, have validated a chemical biosignature in rocks that is used to understand ancient life on Earth. The research provides a new understanding of what Earth’s biosphere was like early in our planet’s history and confirms a reliable biosignature that could be used by robotic or human explorers to look for signs of ancient life on other worlds.
Nitrogen, Earth’s biosphere
The study, published in Nature Communications on Jan. 22 , focuses on a type of metabolism called nitrogen fixation, or diazotrophy. This process is what converts biologically unusable nitrogen in Earth’s atmosphere into molecules that all living organisms use to survive. On Earth, there is a select group of organisms called diazotrophs that can perform nitrogen fixation. This group is a motley crew of bacteria (and a few archaea and eukaryotes) that are found dotted across different branches of the tree of life. Some diazotrophs are free-living organisms that fix nitrogen as they go about their day. Others are symbiotic and survive in partnership with other organisms, living in places like plant roots, lichens, fungi, and even the guts of termites and shipworms. What ties this varied group of organisms together is that they all contain an enzyme called nitrogenase. This enzyme gives them the power to convert …