~3.5 billion years agoReputable sourceWell documented
Photosynthesis and the First Stromatolites
On the timeline · around ~3.5 billion years ago · Archean
What happened
By about 3.5 billion years ago, communities of microbes were building layered mineral structures called stromatolites — among the oldest fossils of living organisms on Earth. Early photosynthetic microbes had begun capturing the Sun's energy, some releasing oxygen as a by-product.
Why it matters
Photosynthesis is the engine of the biosphere; the oxygen it produced would eventually transform the planet and make complex life possible.