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First of all I love this question. My suggestion is that you shuffle a deck of cards, flip them over and note their exact order, then shuffle again and note the order again then keep shuffling and checking the order until the deck resets to the original shuffled order. It’s gotta happen eventually, but it might take you a while. In fact a lot of people have studied that very specific problem and there’s actually really good odds that every shuffled deck you’ve ever held has been the only deck of that order in history. So, yes, it almost certainly has happened somewhere, but good luck finding it.

Life could be forming again RIGHT NOW, but there’s already pretty well established life here already that could stamp the upstart out.

It almost certainly did…

But conditions on Earth were “perfect” for life to exist because this is where all the life we’ve ever seen evolved.

If conditions on Earth was different, life would have evolved differently and people would still say conditions were “perfect” it’s survivorship bias.

So earliest life likely sprung up with some pretty fundamental differences, and whatever evolved best hung around.

We can see modern versions of this when extremophiles overlap due to changing conditions. Life forms that have been isolated thousands (sometimes millions) of years. Or even just the life that exists in deserts for the brief period there’s puddles after a rain.

Earliest life was probably just a bunch of isolated pockets, who were eventually able to evolve and spread out from the extreme environments they came from. Sometimes they take over and spread, others they die out and only the ones that stayed in their extreme environment survives.

The conditions are perfect for life to thrive, and especially to evolve, we’re not so sure about forming.

Actually, I’m pretty compelled by the hypothesis that Mars actually had the perfect conditions for life to form. With less of an ocean covered surface, regular rain, and constant meteor showers. Such meteors would form holes lined with random chemicals, which then get filled with water, forming a puddle. If one puddle doesn’t have all the necessary components to form life, another likely will. That seems to me like a much better scenario than a sparsely diluted ocean on Earth.

Then whatever life originated on Mars might have been thrown into space by one of those meteors, and by chance, fell on Earth. There’s actually evidence that such interplanetary matter transfer is possible, and has happened. That would explain why we only know of a single common ancestor, the only one that arrived here.

Keep in mind that the conditions before life formed were quite different than the conditions once it had already been established. Once life exists, there is a competition for resources. Fewer building blocks will be just floating around and available for spontaneous development of new life and a new replicator will be unlikely to survive in an environment filled with far more sophisticated replicators that have had a head start.

As an aside, see also Silurian hypothesis

“While we strongly doubt that any previous industrial civilization existed before our own, asking the question in a formal way that articulates explicitly what evidence for such a civilization might look like raises its own useful questions related both to astrobiology and to Anthropocene studies.”

For over three billion years, all we know of the evolution of life is from the chemical signatures it left behind, and from the genetic information of the surviving descendants. From that we can conclude that all current life arose from a common origin roughly coinciding with the first chemical signatures of living activity, and the most parsimonious explanation is that life arose on earth only once. But it’s also plausible that some of that early chemical activity was produced by forms of life that arose independently, but were displaced by ours before the emergence of multicellular organisms.

Were perfect. The conditions on earth back when life first appeared were very very different than they are now.

As for how many times it may have happened, there’s no way to know, only that it happened at least once (edit: unless it happened elsewhere and came here somehow).

Behold ty he Life equation. And by extention also the Fermi paradox.

I’m not convinced it’s only happened once.

A new bacterium could have been created in the ocean yesterday. How would we ever know?

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It shouldn’t have happened at all. Abiogenisis is so hugely unlikely, it defies probability.