Often times people have said that alien life could be so alien, that we could be looking at it and not know it.
Then perhaps independent subsequent abiogenesis on this world could also generate life so strange and so different that we could be looking at it and not see it.
First things first, let us define life. I will use the following definition: life is anything that meets all of these three criteria:
1. multiplication: life multiplies on it's own (as opposed to being built only by external forces or being a one-off unique example)
2. animation: life grows and/or moves on it's own (as opposed to being inanimate)
3 sustenance: life requires and takes sustenance on it's own
Rocks are not life as they are born from external forces only, are only moved by external forces, can only split into two or more by external forces, and do not accumulate matter on their own.
Mass-produced solar-powered remote controlled toy cars might move, exist in many examples, take sustenance in form of battery power on their own; but they are not born and do not multiply on their own - rather they are built by external forces only.
A human is life because a human is born of another human, moves and grows on it's own, bears others of it's kind on it's own, as well as absorbs oxygen, water and food on it's own.
A coral is life because a coral is separated from another coral, grows and spreads on it's own, makes others of it's kind, and absorbs oxygen, water and food on it's own.
Abiogenesis is beginning of life, in essence a life that meets all of the criteria, except for multiplication criteria for the first specimen only. This is when external forces build something which from that point onward meets all of the criteria for life.
Suppose a car breaks down in the middle of an intersection. A traffic jam occurs. Surely we would call someone a madman if they said this is abiogenesis happening before our eyes. And yet, I am precisely that madman.
A traffic jam occurs due to external forces - the traffic combined with a catalyst: in this case the break down of a car. This is abiogenesis.
Once a jam has occurred, as traffic flows, more and more vehicles join the jam. Thus it grows. This completes animation criteria.
Should it grow enough to cause a gridlock, it may spread and multiply through budding. Or different vehicles might take different turns and bring to much traffic to another intersection along the way. This finally completes multiplication criteria.
Having completed all of the criteria for life, a traffic jam could very well be called a form of life - one so different that we may have seen it arise, grow, move, multiply and eventually die off; right before our eyes, time and again, and not notice it.
If one says that more cars arriving to a traffic jam is work of external forces only - then also a human or a coral having more oxygen, food and water arriving close to their mouth or cell membranes is also due to external forces only.
If one says that a traffic jam moves because cars move according to traffic rules and that this is due to external forces only - then also a human or a coral moving is due to atoms and molecules in their bodies moving according to external laws of physics.
If one says that a traffic jam multiplies due to external forces of traffic flow - then also a human baby separating from mother occurs due to external forces of scissors that cut umbilical cord. Or likewise a coral separating in two also occurs due to externally caused trauma that separates it in two.
Either a traffic jam meets all of the criterial for life, or humans and corals do not either. Call me a madman if you will, but that's what I think.