[tsimionescu]

If abiogenesis is common, we should expect it to keep happening everywhere around us. We should have noticed at least a few instances by now, given that we have been trying explicitly to produce it.

So at the very least, we can say that the conditions for the apparition of life and the conditions for the proliferation of life seem to be quite different.

Also, given the amount of isolated biomes on earth, if abiogenesis had ever been a common occurrence, i think we should expect for there to still exist some survivors of those other events.

[swebs]

The entire planet is coated with bacteria and bacteriaphages. It's entirely possible that any new life created through abiogenesis is almost immediately outcompeted by evolved microbes.

[tsimionescu]

In today's world, perhaps, but it must have taken vast amounts of time until the first bacteria covered the planet. If abiogenesis were a frequent event on the early earth, there should have been plenty of space for more than one lifeform to survive before life became ubiquitous. And of course it's possible, but it shouldn't be the default assumption either.

[delecti]

What would abiogenesis even look like today? Some random molecules bouncing together in just the right way and spontaneously forming some organic compounds. And then a bacteria comes along and eats it, or it encounters the huge concentration of environmental oxygen and reacts.

Going from inorganic sludge to life isn't "an event", it's multiple events over millions of years until the right chemicals get together and form something that can reasonably be called "a thing" that can even be alive. It only makes sense for that process to have happened once, because the resulting life would have outcompeted any future proto-life.

[tsimionescu]

Sure, that's a plausible account. However, they would only compete if they appeared in a pretty small geographical area. That still leaves it as being a relatively singular event. Maybe much more than once in a few billion years, but still much rarer than many seem to assume.

I would also note that we don't really know of any mechanism that would require millions of years for chemical reactions, or any equivalent of the theory of evolution that would work for hypothetical complex organic substances. Not to say that either is impossible!