Origin of life
A scientific study from 2002 showed that geological formations of stromatolites 3.45 billion years old contain fossilized cyanobacteria. At the time it was widely agreed that stromatolites were the oldest known lifeforms on Earth which had left a record of its existence. Therefore, if life originated on Earth, this happened sometime between 4.4 billion years ago, when water vapor first liquefied, and 3.5 billion years ago. This is the background to the latest discovery discussed above.