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Comment by amelius | Hacker News Reader

Imho, the first explanation is not plausible, because life started really early after Earth was formed (increasing the plausibility that life can spark at any moment).

The second explanation is not plausible because at least we would have found some evidence, i.e., samples of dead and outcompeted life forms.

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Those initial life forms would probably take the form of something like prions, or viruses: small protein assemblies, with a tendency to replicate. They would, almost by definition, have no defences against the armada of today's microbiology roaming every crevice. They would be devoured within seconds of accidentally forming.

Of those that formed billions of years ago, no trace would remain, or, if it did, it would be indistinguishable to us from any non-living molecule that once swam in the primordial soup.

We could test that assumption by synthesizing biological molecules with a different chirality, and dumping them into a soup of "normal" life, and see how much of it remains.

That's a really good experiment to try. I wonder why no one has tried it.

But once started, life will spread quickly and consume the resources needed for sparking life again, making second sparks less likely.

> The second explanation is not plausible because at least we would have found some evidence, i.e., samples of dead and outcompeted life forms.

Does organic material that can exhibit chirality last very long after the organism dies? I thought it pretty much all breaks down to simple molecules and elements within 10 million years or so.

Not if it's in the Hadean Eon; we have serious difficulty finding well-preserved direct evidence from that time. It could be that we settled on DNA and cells before the geologic record was capable of faithfully preserving evidence of either.

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