How are stromatolite fossils evidence of earths early life?

“Stromatolites are pervasive in the fossil record and are some of our earliest examples of life on Earth,” he says. “The microbial mats that created them were predominantly made up of cyanobacteria, which used photosynthesis – like plants do – to turn sunlight into energy while producing so much oxygen over time they changed the early Earth’s atmosphere to make it habitable for complex life.