Panspermia theory?

[Anomalocaris]

I'm still fascinated by the notion that life can only evolve by only one possible genetic framework.
IE, do you guys believe that other life on other planets could have a completely incompatible tree of life to ours?
If so, if panspermia happened concurrently with our own independent evolution, why then, is there only one tree of life?

Did our conditions favour only one? Shouldn't it be the home grown advantage, logically speaking?

Who came up with that notion?

Why do you think panspermia means life arrived here from elsewhere?  Perhaps panspermia means life that arose here went Elsewhere?

We don't really have a good explanation for the appearent genetic affinity shared by all known life on earth.   Maybe abiogenesis on earth is a rather unlikely event, and we are lucky it happened once, and it is too much to expect for it to have happened successfully here twice? Hence all life on earth shared the same origin?

Maybe abiogenesis didn't happen here, and panspermia is also unlikely, but although unlikely it did happen once, but hasn't yet happened again, hence all life on earth share the same origin and are therefore generically related?

Maybe there is Subtle but as yet unknown biochemical reasons why there is only a very narrow range conditions that can give rise to abiogenesis, so although abiogenesis happened many times here, and perhaps also elsewhere and came here through abiogenesis, all life must nonetheless be necessarily so alike biochemically they appear to be related?

If you watch any sci fi movies it would appear the last option is implied by Hollywood to be so.

[mediocrates]

I don't think there's a reason to believe that the source and destination lifeforms of a panspermia event should appear to be related in any way.  They may be biochemically similar initially, but selection pressures in their environments over the subsequent (M/B)illions of years would drive dramatic divergence.

Maybe the only possible way to even guess that they may be related would be to sequence the genome of (recently living or miraculously preserved) samples from both populations to search for similarities left over from their common ancestor.  These could be vestigial genes that are not expressed, but still exist in the genotype of every known living thing.  Until that happens, we can't do anything but speculate.

[Mister Agenda]

Panspermia is an interesting hypothesis that can't be tested yet. Recent discoveries make it seem less unlikely to be the origin of earthly life, but that doesn't make it probable. For what it's worth, the earliest signs of life are found shortly after the Hadean Eon when the crust had cooled sufficiently (though it was still pretty damn hot with lots of volcanic activity) after a lot of pounding from meteorites.

[Anomalocaris]

Actually, I believe recent analysis of zircon crystals dating to 4.2-4.3 billion years ago  suggests the Hadean eon wasn't very hellish at all.   Earth had solid crust, a heat trapping atmosphere, moderate temperature and abundant liquid water on the surface as long as 4.4 billion years ago.  The earliest known life on earth is 3.8 billion years old.  So there is a 500 million year gap between earliest evidence of hospitable environment and earliest evidence of life on earth.

At the end of hadean eon, things on earth actually got much worse. There seemed to have followed a period of unusually heavy meteror bombardment. Age dating of intact ancient rocks shows an abrupt cut off in age coinciding with the end of the period of bombardment, although crustal minerals such as zircon dating to before the bombardment has been found incorporated into rocks that formed after the bombardment. This shows there was a modern looking crust before the bombardment but little if anything sizeable portion of the crust dating to before the bombardment survived the bombardment. But life appear to have arisen very shortly after the end of the bombardment.

This raises intriguing questions.

1. Obviously, did life arrive on the earth through the heavy meteror bombardment? This could account for life appearing to arise so quickly after the bombardment.

2. If life did not arrive but arose through abiogenesis after the bombardment, then it appears abiogenesis is a rapid acting process requiring little time to operate. If that is the case, would life have also arisen in the 300-400 million years of pleasant watery warm environment that appeared to prevail before the bombardment?

3. If life did arise before the bombardment, was it sniffed out by the bombardment, or did it survive the bombardment and reemerge quickly after the bombardment?

4. If life did arise in earth before the bombardment and survive the bombardment, this implies early life is extremely resilient and have good chance of hitching a ride on ejecta from the bombardment to land elsewhere in the solar system.

[Gawdzilla Sama]

I'm still fascinated by the notion that life can only evolve by only one possible genetic framework. 

Who says that?

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pan·sper·mi·a
panˈspərmēə/Submit
noun
the theory that life on the earth originated from microorganisms or chemical precursors of life present in outer space and able to initiate life on reaching a suitable environment.

[ignoramus]

no-one ...
I'm asking what people's thoughts on it are. (nothing to do with panspermia)

[Gawdzilla Sama]

no-one ...
I'm asking what people's thoughts on it are. (nothing to do with panspermia)

[Edwardo Piet]

I think they're just following the evidence.

All things being equal it would seem more likely for life to originate locally.

But all things are not equal... there is evidence of meteorites landing here and I'm guessing they've found sufficient evidence to believe it contained simple lifeforms (or the precursors or beginning conditions to simple lifeforms)... so it's more likely life originated elsewhere.

Of course this begs the question of how life began there... but that's still a different question.

[Gawdzilla Sama]

We can come up with all kinds of theories, some reasonable, some just stupid, but we have no solid proof for any of them at this point.