If conditions on earth are perfect for life to form shouldn't have happened more than once?

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.

For all we know it did. We believe that the Earth is 4.5 billion years old but it's estimated that conditions suitable for life only appeared about 200 million years after that. Since the oldest fossils we've found are 3.7 billion years old, there is a 600 million year gap between when we think life could have formed and out earliest records of it.

There is every possibility that life formed multiple times in different environments on Earth in those first few hundred million years and then been wiped out by one of the frequent cataclysms that ravaged the early Earth. We have no way of knowing though. If life formed around a volcanic vent and then got wiped out by a meteor impact there would be no evidence it ever happened. Even if such life was wiped out by a climatic shift or something like that, there still wouldn't likely be much evidence left if any right now. The Earth's surface has been changed so much in the last 3.7 billion years, there are very few areas older than that where such fossil records from before that could be found.

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.

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.

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."

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.

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?

I don't have the answer but what an interesting question!

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).

Life has to start pretty simple. Chains of very basic molecules, that kinda self replicate. Those molecules would be tasty nutrients without any evolutionary self defense mechanism. So anything like that would be immediately eaten by the stablished life forms. No chance for enough self replication to evolve into anything.

Our current life tree have had many million years of evolution, we all are perfect killing machines. No proto life have a chance.

I believe it did happen more than once. The reason why life on Earth has developed into such complexity is that the primordial soup, where life developed out of, has been cooking undisturbed from events like supernovae and such that would have wiped out everyhing (Earth istself as well as the whole solar system) nearby. Life could develop over several billion years, and cosmic events like asteroid impacts didn't wipe out all of life. Remaining life startet over again.

If life developed on another planet with similar features like earth, it could have been wiped out by a nearby supernova, by a collision between two planets and similar events, before it got any more complex.

The conditions of the early earth was very different compared to today’s earth. Particularly after photosynthesis was formed.

There is no way to know other then going back doctor who style, there's plenty of other ideas for you to consider, Stargate had the ancients, there's also a show called the 100, Homeworld games had their own thing, this could be where we evolved or this is a prison planet or a farm like in the Skyline movies or we crashed here on space Titanic, so many theories but no way to know for sure...

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