@FatherOfNyx -- The main supporters of panspermia who are not hanging on to the creation nonsense consider that there probably was not enough time between when the Earth cooled enough to permit abiogenesis to take place and when we have good evidence for the emergence of life. I find this interesting primarily because they have no workable argument for their position.

I have no trouble accepting the notion of panspermia. In some ways it is rather a good way to account for that short available time here on a cooling planet, even though the process of abiogenesis could have (since I'm shouting out grand speculations) occurred on the very day conditions would permit it. The one element of panspermia that I find most fascinating is the Directed Panspermia proposition. As a Science Fiction writer, that notion provides a lot of fodder for some fine stories. As a scientist, I remain skeptical but open to the idea.

@evidentialist In all honesty, I think you think that panspermia supporters support panspermia without rejecting an original abiogenesis because that's what you think. I am totally ok with the idea of panspermia, but I've seen way too many supporters of panspermia who flat out reject abiogenesis as even being possible. It's the shortsightedness of the masses, the people who don't really research the topic but want to form a belief around it. You don't seem like one of those people.

I don't reject panspermia, it's a plausible possibility. I am more of a fan of soft panspermia, the idea that at least one, if not several, of the building blocks of life had a space-based origin. I would even say that it is highly likely that many of the precursors to life were forming in the protoplanetary disk before Earth even formed. I know they ran computer simulations of this before as well and it seemed likely. If that were the case, then it was really just a waiting game for Earth to cool and get the ball rolling under the right conditions.

Out of all the different possible types of panspermia, I'd say the most likely would be soft. The type with the best chances statistically (aside from soft) would be directed.

@FatherOfNyx -- I didn't say anything at all like what you interpreted. I am a scientist and what I think about things is guided by those principles. Panspermia is an interesting and completely plausible proposition. Believers are opposed to it because, well ... Big Creator Dude in the Clouds. Some scientists oppose the notion because they think the case for local abiogenesis is undeniably strong. Where I agree that the case for local generation of life is likely, I am not opposed to panspermia. In fact, I find it rather fascinating in many respects.

I agree with you that the most likely scenario is the Ballistic Panspermia proposition. Most of the needed molecules, including more amino acid chains than are on Earth exist in our local space and could easily have drifted in through the deep time between collision with Theia and Earth cooling enough for abiogenesis to begin. My imagination would like it to be Directed so that I can justify my current work about our "parents" coming to see how the "kids" are doing.

@evidentialist I don't think many scientists reject any and all forms of panspermia. Most scientists seem to agree that some of the building blocks of life had a space based origin. Thing is, it was the conditions on Earth that brought all the building blocks, both space based and Earth based, together. I have yet to hear a scientist say that all of the building blocks formed exclusively on Earth. Many of them did form on Earth, but we know some formed outside of Earth.

I have no idea why you are saying that I said ballistic panspermia is the most likely. It's actually the least likely. For a fully formed life form to form on another planet that was then destroyed, and then for life from that planet to survive a trip to Earth, the chances are astronomical. The idea of life being deliberately seeded on Earth by aliens is far more likely than ballistic panspermia which relies on random chance. Even with the existence of aliens not being proven, it's far more likely then ballistic.

@FatherOfNyx -- Ballistic Panspermia is what you referred to as "Soft" Panspermia. It is the same thing. When a microscopic bit of dust enters our atmosphere it is entering ballistically. It is an important distinction when we're talking about abiogenesis regarding where the constituents in that process came from. There are plenty of scientists who say all the constituents for life were part of the forming Earth. They are the ones who say life is homegrown. It becomes mincing words when one says that technically all the constituents of early Earth came from space and therefor panspermia is the answer.

What the proponents of panspermia are saying is that it required some kind of input from space in order for abiogenesis to occur here. Very few suggest that living organisms were brought here either naturally or transported by someone else. There is too much evidence to the contrary. Granted, it is thin evidence, but it is there. What they are saying is that the cloud of gas and dust from which our star and those within 20ly to 50ly were formed probably was home to molecules required for life and that our planets and any others around other local stars were likely seeded from that cloud. For this there is ample evidence as well.

[newscientist.com]

Iso-propyl cyanide has been detected in a star-forming cloud 27,000 light-years from Earth. Its branched carbon structure is closer to the complex organic molecules of life than any previous finding from interstellar space.

The discovery suggests the building blocks of life may be widespread throughout our galaxy. Various organic molecules have previously been discovered in interstellar space, but i-propyl cyanide is the first with a branched carbon backbone. The branched structure is important as it shows that interstellar space could be the origin of more complex branched molecules, such as amino acids, that are necessary for life on Earth.

[phys.org]

[astronomy.swin.edu.au]