What do scientists consider the first stage in the origin of life?

The first life probably appeared several hundred million years after Earth was formed as a planet in the early solar system 4.5 billion years ago. There is plenty of evidence to support this claim, but the fossil record is the easiest to understand. Even bacteria leave fossils, and such micro-fossils have been found in Australian rocks that are about 3.5 billion years old.
Scientists know that the Earth was very different when life began. For example, a large number of craters on the lunar surface were created by giant impacts from comets and asteroid-laden objects that were part of the accretion process that formed the moon. The collisions continued approximately 3.9 billion years ago.