system
Given the following post, respond as if you're commenting on Reddit:
human
If Earth has the conditions for life to be created, why did it only happen once?

Layman here so forgive me if I'm mistaken.

My understanding is that all life on Earth originated from a single common ancestor and shares the same DNA, so logically (?) there was a single event that triggered the spontaneous creation of life that eventually evolved into every living organism that has ever existed on this planet. 

My question is, if the conditions on Earth are perfect (or were perfect?) for abiogenesis to occur, why has it only happened once?
gpt
We don't know.

We don't know if it's happened just once. We cannot form a complete characterization of the conditions on Earth throughout the Hadean and Paleoarchean to begin assessing how many times life may or may not have arisen.

It may have happened numerous times. The lineage in existence today may simply have been the only one to survive the Late Heavy Bombardment.

Maybe the emergence of DNA represents a major punctuated episode - perhaps the single greatest leap forward that life on this planet has ever seen - that outstripped and out-competed all other forms of proto-life.