Has an abiogenesis occurred
Why did abiogenesis only occur once?
However, it can never happen again as all life forms on earth today are similar at the molecular level (DNA), suggesting a common origin.
An important distinction is that everything existing Life on earth has a common origin.
It is entirely possible that abiogenesis occurred many times, but any organisms it created died out early or are not preserved in the fossil record.
Immediately after the first spontaneous abiogenesis, the environmental conditions on earth changed dramatically and made a repetition impossible.
No The red bands and the dating techniques that follow suggest that it is very took a long time to change.
The first organisms to emerge consumed all subsequent organisms ...
Possible, but we have solid data to suggest that the first functional organisms were autotrophs. That said, they made their own food out of whatever they were exposed to, and the predator-prey relationship hadn't yet played a major role.
The theory of common origin is actually wrong, despite the similarities between organisms, and abiogenesis occurred several times in the same way.
The Common Origin Theory - as you defined it - is almost certainly true. DNA is a constant, just like RNA, mitochondria, etc.
However, this does not mean that abiogenesis could not have happened more than once. As I said above, the Common Origin Theory applies to existing (living) species, not necessarily all organisms that have ever existed. Species are constantly dying out.
After all, spontaneous abiogenesis never occurred on Earth because conditions never allowed it; Instead, a proto-organism came to earth from a planet where conditions do so (panspermia).
That only pushes back the question of abiogensis a little. Then why did it evolve on another world and not on earth? How did it survive in space? Why was it so good for Earth's environment when Earth-like planets are rare (relatively speaking)?
The standard theory of geological history is wrong (i.e., the earth was in a "fertile" state for much longer than is generally believed, prior to the final origin of life, because an unknown mechanism caused radiometric dating to give incorrect results).
Estimates and conclusions come from more than radiometric dating. We have fossils, geological records of continents, and even ice core records from the Poles that both confirm radiometric dating and establish themselves as independent evidence.
Neither of these seems likely to me, but even less likely I find the idea that life arose spontaneously almost immediately (within a few hundred million years, possibly even faster) after the earth's crust solidified, and never again after.
What are the current theories on this subject? Both random speculation and references to relevant publications are welcome.
This SE is not the place for random speculation. I don't have any publications on hand so I can return my response and edit it when I get the initiative.
The most popular theory is that, with a few possible exceptions, all life evolved from a single organism that existed billions of years ago. This organism may or may not have been the only one. If it was one of many variations of precursors, we have yet to find the precursors in the fossil or biological records. Given the extremely long time span between now and the beginnings of life, we do not expect fossils to exist from all organisms that existed around 3 BYA. The best we can do is speculate about what existed could, to explain what we have see today.
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