“I doubt if we will ever know how much of life’s chemistry originated on Earth, and how much, if any, was “seeded” from somewhere else.”
The evidence would appear in the form of critical differences versus similarities in the etiology of their structures and functions, ranging from energy usage and chemical pathways to homochirality for just two of innumerable examples.
“Today we only know evidence suggesting 400 million years from Earth’s formation to first possible life.
That’s a long time — for example: 400 million years ago was still Early Devonian epoch, a good time for sharks, but no land animals or birds yet.
A lot can happen in 400 million years.”
That is not entirely true, insofar as there are competing lines of evidence that allow the origin of the organic precursors of Life and Life itself to have occurred billions of years before the Sun and Earth came into existence. There is no reason why Life could not have originated on another planet 8 billion years ago orbiting around a star which subsequently which obliterated itself and the planet in a supernova. Life may have survived in the silicate fragments of the planet and become incorporated into the nebulae from which the Sun, Solar System, and the Earth were formed. Life also may have originated inside the nebulae of interstellar space just as some organic precursors to Life have already been discovered in these nebulae. So, the origin of the Earth can in no way be regarded as the only potential for the origin of Life on the Earth.
“So, were extraterrestrial “seeds” planted here?
Maybe, but maybe not.”
“I’d go with “maybe not” until somebody proves otherwise.”
I have to go with the laws of physics, chemistry, and biochemistry which leave the door open to the origin of Life being anywhere and anytime the necessary chemical and biochemical reactions can take place; which at this time appears to be anytime after the nucleogensis of the chemical elements necessary for Life; including Carbon, Silicon, Nitrogen, and Oxygen, among others. More than 55 years ago I argued that exoplanets must exist in numbers far greater than the stars by implication of the laws of physics, despite the fact no exoplanets had yet to be discovered. I predicted it was only a matter of time and better technology before we would discover those exoplanets implied by the laws of physics. Half a century later I have been proven to be correct about the existence of exoplanets. I’m confident the exobiology research will do likewise for the discovery of extraterrestrial Life and the origins of Life on the Earth, because the evidence appears to imply the organization of Life from the building blocks of the Universe is inherent in the natural characteristics.
WhiskeyX:
"The evidence would appear in the form of critical differences versus similarities in the etiology of their structures and functions, ranging from energy usage and chemical pathways to homochirality for just two of innumerable examples." 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.
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.
WhiskeyX: "There is no reason why Life could not have originated on another planet 8 billion years ago orbiting around a star which subsequently which obliterated itself and the planet in a supernova."
Of course, no dispute: all that is possible, I'm only saying, until there is convincing evidence, it cannot be presumed, or assumed.
WhiskeyX: "More than 55 years ago I argued that exoplanets must exist in numbers far greater than the stars by implication of the laws of physics, despite the fact no exoplanets had yet to be discovered.
I predicted it was only a matter of time and better technology before we would discover those exoplanets implied by the laws of physics."
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.
