No. We weren't there to observe it. Many believe that to be the case by extending current scientific knowledge into the distant past.

: It took time for the universe to cool enough for particles to form. Even then
: it was a plasma of protons, neutrons and electrons.

Believed to be.

: Later there was mostly hydrogen, some helium and trace amounts of Lithium.
: There was no carbon, nitrogen, oxygen, phosphorus, calcium, sodium, or
: sulfur. These came later, formed in stars and seeded throughout the
: universe by stellar explosions. So we know that life didn't always come
: from preexisting organisms because organisms didn't always exist.

No, you believe that to be true, because you weren't there, and no one else was. The framing of the events you describe have, as I've explained, not been observed and repeated, only presented together as an explanation of past events that must be trusted as truth, based on presumptions about the past. However "reasonable" the explanation may be, it is none-the-less, an explanation, not a direct observation.
And I fully expect you think I'm stupid or ignorant for not jumping on the bandwagon, and for thinking critically (which btw does not include disbelief) about any explanation of past events, whether yesterday, 1000 years ago, or 1 billion years ago. It simply means realizing that any explanation for an unobservable event - no matter how reasonable the explanation - may change at a moment's notice.

: You don't need magic to have life.

Do you believe in magic? I don't. I just believe what I see.

: Life can be life, it doesn't have to have a spark - whatever that is. It adds
: nothing to what is already there.

And yet, we have this term "biological" which is a basic term we use to refer to things that are classified as "living organisms". So. How do you separate biological from non-biological? Seems like you're saying there is no difference. Scientists say otherwise.

: Essentially you are saying that people are shit, animals are shit and the
: universe is shit. All that we see is nothing - only the presence of a
: magic spark gives us worth.
: Our opinions, actions, thoughts, bodies - all shit.

Um. No. And don't put words in my mouth.

: My opinion is that what we see is enough.

And that's fine. First, you're free to hold that opinion. Second, I fully agree that scientifically speaking, observations are the best way to prove something irrefutably. What we see is enough. What we don't see we are free to theorize about, to attempt to explain in the best way we know how. And/or to trust what others say about it.

: people matter to me irrespective of
: whether there is something that we can't detect. What we can detect is
: enough for me.

Right. Observation. Repetition. Experimentation.

: My feelings, my actions, the thoughts and actions of others
: are enough for me to care about them.

Ok

: I don't have to invent fictions in order to respect other people.

What on earth are you talking about? Respecting other people? Who's disrespecting other people?
I presume you're talking about whether something needs to be 'alive' for us to respect it as life. But again, if you don't believe there's any difference between a rock and a person, fundamentally, then by what standards can you dictate we as humans must respect each other more than we respect a rock? Actually, I digress - that's a great moral topic on which to base some scifi (at least that I would find interesting).

: What would you do if we detected this vital spark? What would you do if we
: understood it? Could generate it? Convert it to and from electricity? Knew
: its units and understood its physics?

Good question for science fiction. Like the Matrix. At this point, not reality.

: Would you say that if we were just vital spark then we were nothing?

Eh?

: We understand chemistry, we can do the math. Does that make chemistry shit?

I do not understand why you keep bringing shit into this discussion.

: Why would being a product of chemistry make people worthless in your eyes?

When did I ever say or imply that is what I thought?

: Do you not respect what we know and experience of people as they are?

You're reaching at something and I have no idea what. I have said absolutely nothing about respecting or disrespecting anyone, regardless of chemistry or 'vital spark'.

: I don't think that inventing fictions helps one iota. It doesn't make us any
: deeper or better as people. Would you stop respecting people if we could
: make them in a machine? Would people loose their worth to you?

Science fiction. Explore it.

Heck, the upcoming movie Her is dealing with that subject matter; a digital AI becoming so real, so indistinguishable from a real person, that the man falls in love with her (and vice versa).

:: If you have no convincing evidence that X does not exist (let alone any
:: proof), let's just assume for now that it does.
: No, definitely not. That way lies madness. We would have to accept all
: propositions - especially the more formless and non-nonsensical ones (the
: hardest ones to understand or reason about).

No we wouldn't.
I could likewise say, if we assume that it does not exist, we would have to deny all propositions that seek to prove that something unobserved exists. That way lies madness.
It is most certainly not a matter of "accepting all" just because we think critically about one. There's no reason to extend some extreme action to all things anyone proposes. That's ludicrous. Everyone simply decides among viable explanations what they believe is the most feasible, based on their own observations. That's the way we work. Denial of personal observations is an entirely different problem, which generally requires medical or psychological help. But if there are no observations to be made, it becomes a matter of trust and/or belief, whether "reasonable" or not.

: No. A is a positive claim. Not A is a negative claim. The burden of proof is
: on the positive claim.

Not even worth responding to this, again.

: By default we reject positive claims until we are presented with sufficient
: evidence to take them seriously. It is a time saver and a bullshit
: reducer.

Positive claims extend from an axiom, from a starting point. If the starting point is 'general understanding is this is correct' then anything claiming otherwise has the burden of proof.
The reason we say you can't proof a negative is because of that 'bowl' analogy. We don't have the ability to observe the entire universe, and so no, it is not possible to prove the negative in that context. But a fish bowl? You most certainly can prove the non-existence of a fish in the bowl, because you can see the entire bowl; you as an observer are outside the conditions of its existence and so can either prove or disprove both postulates - "a goldfish is in the bowl" or "there is no goldfish in the bowl".

: Doesn't work when the claims involve the existence of things that we can't
: demonstrate. For example: there is an invisible pink unicorn in the corner
: of the room. And in addition: it is inaudible, intangible, has no smell
: and gave mankind intelligence. Please disprove.

See previous comment re being an observer inside the fish bowl vs outside. (which you so conveniently left out of your other reply)

: Or

: The harmonious colors of the rainbow gives us our harmonious sense of
: morality. Disprove! Bonus points for disproving without recourse to
: personal incredulity.

Disprove? A="harmonious colors of the rainbow". B="harmonious sense of morality". Observe that every instance of A coinciding with B was in fact due to a mediator C and not A, and that A necessarily does not give us B. Bonus points for showing instances where C and A coincide without B.
If we had an observation perspective outside the bounds of all of A's existence, then we could disprove the statement. As we don't exist outside the bounds of the rainbow's existence to observe all rainbows in space/time, and since culture generally considers morality itself entirely subjective if it even exists, your question is facetious and argumentative. Irrelevant.
The goldfish in a fishbowl analogy is far more relevant.

Seriously, it's like you're arguing just for the sake of arguing now.