Did life on Earth start on Earth, or did it start on Mars and move to Earth? If you frame such panspermia as an “extraordinary claim” for which you demand “extraordinary evidence”, you will of course conclude that this should be treated “skeptically” as unlikely and sloppy unscientific “speculation”. To be disdained and not treated as serious by respectable academics and science journalists. But that’s not really fair.

You see the early Mars environment is, a priori, about as likely a place for life to start as the Earth environment. So if the rate at which life is transferred between the planets were high enough, then equal chances of life starting first in both places would result in equal chances for Earth life to have started in either place. We should take the expected time difference between life starting in the two places, and ask how high is the chance that life would move from one planet to the next during that period. The more often rocks are thrown from one place to the other, and the more easily life could survive for the travel period within those rocks, then the more likely it is that Earth life started on Mars.

In addition, Mars, being further from the Sun, would have cooled first, and had a head start in its window for life. Making it more likely that life would start there and spread to Earth than vice versa. Of course life starting first on Mars would have implications for what we might see when we look at Mars. If we had expected Mars life to continue strong until today, then the fact that we see no life on Mars now would be a big strike against this hypothesis. But if we expected Mars life to have died out or at least gone dormant by now, then the issue is what we will see when we dig on Mars. With enough data on such digs, we may come to reject to Mars first hypothesis even given its initial plausibility.

A similar analysis applies to panspermia from other stars. You might think it obvious that the rate at which life-filled rocks from a star make it to seed other stars is very low, but most stars are born in large groups close together in stellar nurseries. So if life arose early enough within our star’s nursery, there might have been high rates of moving that life between stars in that nursery. In which case the chance that Earth life came from another star could also be high, and the best place to look for life outside our star would be the other stars from our stellar nursery.

Now consider the possibility of lost advanced civilizations. Not just civilizations at a similar level of development to those around them in space and time; that’s quite likely given that we keep finding new previously-unknown settlements and developed places. No, the more interesting claims are about substantial (but not crazy extreme) decreases in the peak or median level of civilizations across wide areas. Such as what happened late in the late Mediterranean Bronze Age, or at the fall of the Roman Empire. Could there have been “higher” civilizations before the “first” ones that we now know about in each region, such as the Sumerians, Egyptians, and Chinese Shang dynasty? (I’m talking human civs, not others.)

Yes, you might think of these as “extraordinary” claims for which we lack extraordinary evidence, and declare them unlikely and sloppy unscientific speculation, to be disdained by the respectable. But again, that’s not fair. A priori it is nearly as likely that overall advancement in a region would have taken a big (but not crazy huge) temporary dip, as that it would have had a recently-typical rise. No, that isn’t much of a reason for skepticism.

Substantial, if hardly overwhelming, supporting evidence comes in the form of writings from the earliest authors we can find, who explicitly claim that they descended from more advanced prior civilizations, who fell due to big cataclysms. This story is actually quite common. Further supporting evidence exists when the earliest versions of the first civilizations we see had surprisingly advanced abilities for their time in key areas, abilities which then declined over time. That is what you’d expect to see after a prior peak. And that does seem to be what we see in Egypt and Peru, as far as I can tell, regarding stone masonry abilities. Of course that might also just reflect local fluctuations in particular abilities; the big question is how much correlation to expect to see across different kinds of civilization abilities.

The most common contrary evidence offered is the absence of expected supporting evidence. For example:

No matter how devastating an extraterrestrial impact might be, are we to believe that after centuries of flourishing every last tool, potsherd, article of clothing, and, presumably from an advanced civilization, writing, metallurgy and other technologies—not to mention trash—was erased? Inconceivable. (More)

He claims that glacial runoff from the comet’s incineration of the ice sheets covering North America could have destroyed every trace of civilization, though how animal bones survived but not a single stone or metal tool, or a single indisputably human-carved block of stone is beyond me … Clovis people left behind tens of thousands of stone tools and fluted points, while Atlantis is represented by exactly nothing. Even if their bones turned to dust, where are their stones and their metals? Where is the pollen from their crops…? (More)

Here the key question here is: what sort of historical evidence should you expect to have already seen, if it were really there? On the one hand, we clearly have seen enough to safely conclude that there aren’t large dinosaurs roaming the streets in our major city centers. On the other hand, we often hear reports of people uncovering old things that others had pretty confidently predicted would never be found. Which makes many suspect widespread overconfidence in claims about what we know can’t be there, because if so we would have seen them already.

Yes, the bigger and more techy a lost civilization one postulates, the more likely it is that we’d have seen evidence of it. For example, the bigger a civ, the earlier they adopted pottery, and the more widely they used it, the more we should expect to find pottery shards. Similar for widespread use of metal. But if there are plausible civ hypotheses that don’t require them to be as big, or as much into stuff that creates long-lasting evidence like pottery shards, then the more trouble we’ll have rejecting such hypotheses.

One complication re lost advanced civilizations is that the last 7K years have seen especially calm weather worldwide. Before that, sea levels changed a lot more, and before 10Kya temperatures changed a lot more, and much of the Earth was covered with glaciers. There may even have been some huge worldwide cataclysms around 12Kya. All this made it harder to sustain complex civilizations back then, but also made it harder to preserve evidence of them for us to see now, if they has been there.

Seems to me we want something like prediction markets here, to give better incentives and aggregation re predictions of what stuff will be found where re when. So let me suggest: markets in archeology prize obligations.

First, let’s set up some archeology prizes, each of which pays $P to the first group who can show an X found in region R from before date D. For example, show a homo sapien skull found in the Americans dated before 200Kya. Define $P in units of some standard investment asset, like the S&P 5000 or MSCI All Country World Index. Then create markets where people can be paid in those same units to take on fractions of prize obligations. For example, someone might be paid 10 units to take on an obligation to pay 100 units of the pre-200Kya America skeleton prize.

The asset ratio price in these markets, such as the 10% ratio of 10 to 100 in the example above, could be interpreted as a probability that the prize will ever be won. With enough kinds of prizes for enough findings X, regions R, and dates D, we could get a pretty good picture of what we are likely to find. Such as lost advanced civilizations. These prize payments would encourage more archeology effort to discover things.

Skeptics who see little chance of dramatic findings might eagerly be paid to take on such obligations, while enthusiasts who see such discoveries as more likely could take the opposite sides of such transactions. Each side can expect to profit by reversing their trade when the world comes to its senses and agrees with them, which might happen long before any actual discoveries are paid prizes.

Investigators who expect to be able to show particular findings soon might offer to pay now for others to take on obligations to pay bigger related prizes later. And these relative prices might give investigators hints about what to look for where.

As it is quite legal to pay out prizes and to transfer obligations to pay prizes, all of this looks pretty legal to me. (But I’m not a lawyer, so of course not legally allowed to state opinions on such things.) Yes, you’d need to set things up to ensure that people will make good on obligations to pay prizes, but that seems feasible. We could get even more trading if anyone were allowed to pay to become an auxiliary prize recipient in case a prize was one by someone, but I’m less sure that would be considered legal.

So, who wants to help set this up?

Added 9a: During the classic Egypt era, many monuments were built over and near apparently much older sites with much older monuments built using apparently advanced tech. Many of these older sites have very large tunnel systems, many of which are from being fully explored. That is my best bet re where to look for evidence of lost advanced civs.