The main characteristic of life on our planet is that evolution created all the building blocks of life as we know it today. It is the corner stone of biology. Just like the chicken and egg question, scientists have asked, what came first, life or evolution? Here is an interesting article on some mathematics around this very question!
This question is not a new one. In fact 32 years ago Richard Dawkins wrote his book “The Selfish Gene“, he talked about selection on genes and how they played a major roll in life on our planet. He also talks about replicators(earlier versions of RNA/DNA).
When did life start on the planet? What kind of organism was it? Was it single celled? The answers to these questions are not as important as replicating. Dawkins states that the ability to replicate, and reproduce was the start of natural selection in the primordial soup. It is more important to understand that, than argue about a definitive moment that we would consider life starting, as that could be debated ad nauseam. If you think about it, with various chemicals and amino acids forming chains with existing finite resources, a replicator that could reproduce a copy of itself had a huge advantage.
It effectively never died, as it passed on the code to successfully reproduce itself from the resources.
So essentially our definition of life starting should be when one of these chains was successfully able to replicate due to some mutation. Not so glamourous…I do recommend you pick up a copy of The Selfish Gene though. You can find it online as a free e-book. It stands the test of time.
I have an evolution based comic from cectic.com for you! Enjoy!