“There’s no reason to presume (or assume) that if we discover evidence of life on, let’s say Mars, that such life didn’t originate on Earth and travel to Mars via some rock from a meteor impact. There’s no particular reason to presume the reverse.”
That’s correct.
“What we know for certain today is that whatever precursors of life, if any, arrived on Earth 4+ billion years ago found a happy-home here and evolved continuously ever since.”
Yes, precursors to Life or Life itself.
“Of course, no dispute: all that is possible, I’m only saying, until there is convincing evidence, it cannot be presumed, or assumed.”
Yes, but the more important aspect of the issue are the many implied evidentiary reasons why extraterrestrial origin/s of Life on the Earth older than the Sun and Earth “cannot be presumed, or assumed” in the present absence of conclusive evidence for or against such conclusions. Just because we have not yet been able to explore the evidence and discover it does not mean the evidence implied by what little we do know won’t be there when we do finally obtain the means to discover it. Too many commentators adopt the logical fallacy that the absence of evidence due to limited observational capabilities is conclusive evidence the evidence does not exist.
“Fifty-five years ago I was an avid reader of many sci-fi books, all of which assumed there were numerous distant stars with earth-like planets. Such predictions took no great genius, FRiend.”
Agreed, you would have thought it “took no great genius....” It was a concept older than all of us today, yet it was still a much ridiculed prediction 55 years ago. A teacher invited I and another student to travel to a special evening university lecture by a noted professor in chemistry and organic chemistry regarding human interstellar travel to the exoplanets in other star systems. What was especially remarkable about the event was the way in which he trashed the ideas of human interstellar travel and any assumption that exoplanets must exist. The teacher, a WWII Army Air Forces combat veteran, was amused by my visible frustration listening to the professor carry on. Thanks to the 1950s era science fact and science fiction books I had been reading, I knew full well the professor was spouting nonsense. Interstellar travel was theoretically possible using asteroids as generational interstellar transports and exoplanets were and still are inherently implicit alongside the physics forming any star from a nebula. Despite the obvious evidence and logic, the concept of exoplanets remained controversial even among the professors of acaddemic science who should have known better 55 years ago. The teacher who invited us to attend the lecture was pleased to see us young students challenge the university professor’s conclusions.
To my knowledge, nobody had concluded anything yet.
This particular site lists seven different theories of abiogenisis, including panspermia.
And this site provides a lengthy discussion on the whole subject.
The real fallacy, imho, is in calling any of these ideas scientific "theories" -- in fact none of them are real theories, all are at best hypotheses of which only some can be actually tested.
Of course, nothing wrong with scientists taking their best SWAG at what is currently unknowable, but we should not give such notions more credit than they deserve.
WhiskeyX: "...yet it was still a much ridiculed prediction 55 years ago.
A teacher invited I and another student to travel..."
Hmmmmmm... I was also invited on such a field trip, but not in science, in student government.
It was a session of the "model UN" in San Francisco, a very long drive for what turned out to be a disappointing experience.
Left me with a lasting impression of how much I dislike the United Nations.
Funny how these things work.
Have a great day, FRiend.