Four Cases for Panspermia
Star formation peaked around 4Gyr after the Big Bang, Earth formed around 5.5Gyr later, and Earth is now 4.5Gyr old. The usual theory is that life arose within Earth’s first 0.4Gyr, but another possibility is that life first arose on a planet Eden around a star that formed near that 4Gyr peak. A rock then smashed into Eden, kicking off another rock holding life, which drifted to seed Earth’s stellar nursery.
The main argument against this alternate scenario is the apparently rarity of kicked-off rocks landing on other planets while still holding life. And this is in fact a pretty strong counter-argument. But four pro-arguments are worth noting.
First, the earliest Earth life what we know of looks very complex. So either that early life was actually a lot simpler than it looks, or complexity increased far faster at first than it did later on, or life evolved for billions of years before it arrived on Earth. At least one numerical analysis of complexity supports this argument.
Second, our grabby aliens analysis suggests that life on Earth was crazy lucky; it has nearly achieved a level of advancement that only one planet per million galaxies ever achieves. The chances of doing this go as a power law of time, where the power is the number of hard try-try steps at which life must succeed to reach our level. Time durations in Earth history suggest there were roughly six hard steps. Thus if life evolved previously on Eden for a similar time period, that predicts roughly twelve hards. And thus due to the power law that Eden hypothesis is favored by a factor of 2^12 = 4096 relative to the Earth-only life scenario.
Third, as the number of stars seeded in our stellar nursery would have been proportional to the size of that nursery, the chance that it was seeded with life increases linearly with its size. And it turns out that, as predicted by the panspermia hypothesis, our nursery was very large:
Nebula Barnard 68 … Only half a light-year across, it has barely enough material in it to make a single star slightly heftier than the sun. … On the other end of the scale we have the Orion molecular cloud complex, …many hundreds of light-years across. It's beefy enough to make a staggering number of stars—at least 100,000 like the sun.
Their results indicate that as it formed in its natal disk, the early sun was probably pummeled by powerful winds and supernovae explosions—both arising from massive stars. That means the solar nursery was more like the Orion complex than Barnard 68.
in late 2022 a different team of scientists published a paper in the journal Astronomy & Astrophysics investigating a similar question. The researchers reason that at least one supernova must have exploded near the still-forming solar system to create the radioactive elements seen in ancient meteorites, so—because of the relative rarity of such events—they conclude the sun's birth cluster must have been very large to ensure, statistically, that this could occur. (more)
Fourth, many report strange UFO observations, the most dramatic of which seem hard to explain as honest mistakes. So either there has been a huge long-term well-coordinated hoax, some Earth org has keep amazing tech secret for a crazy long time, or there really are aliens visiting. And the most plausible way to explain those aliens visiting here now, while the universe around us still looks empty, involves postulating that such aliens are our panspermia siblings.
Am I missing any other big arguments here?
Could bacteria really survive the impacts needed to transfer from one planet to the other? You mention "six hard try-try steps" but it seems like the transfer would involve hurdles at least as difficult as that.
First a huge asteroid has to smash into Eden hard enough so the chunks reach escape velocity not just from Eden but from Eden's star. If Eden and Eden's star are like Earth and the Sun, this means the chunks have to be blasted loose at more than 40 km/s. Wouldn't the chunks be molten after an impact like that, killing any bacteria that might have been on them?
Then the chunk has to travel for a very long period through space. It's plausible that some bacteria could do this, but now they have to be bacteria capable of surviving extreme temperatures and shocks, *and* capable of surviving space for millions of years. This adds more "try-try steps."
Then the chunk has to be lucky enough to "find" Earth. That's more "try-try steps."
Then the chunk has to impact Earth. Since it came from outside the Sun's gravity well it therefore would have gathered 40 km/s of extra speed, in addition to whatever speed it had in interstellar space, as it fell from there to Earth. This makes it a much faster and harder impact than most asteroids that hit Earth. The most likely outcome is the whole asteroid would burn up in Earth's atmosphere (another try-try step). If the asteroid was too large, then it would pass through the atmosphere and hit the crust with the force of millions of fusion bombs, like Chicxulub, immediately turning to vapor and liquid and leaving no chance of survival for anything on it. If the asteroid is *just* the right size, then *maybe* only the outer layers would burn up in the atmosphere and perhaps it could be slowed by the atmosphere enough to reach the ground intact. Only bacteria on the *inside* of the asteroid could possibly survive this.
Then the bacteria has to be capable of thriving in the chemical environment of early Earth, which is surely different from the chemical environment of its home Eden.
So the bacteria that would survive it has to (A) be capable of surviving energy release like that in a nuclear explosion (B) be capable of surviving interstellar space for millions of years (C) thrive deep *inside* rocks (D) be so astoundingly lucky that it hits Earth (E) be so astoundingly lucky that it does so deep inside just the right size chunk to settle to the ground non-violently despite a speed greater than 40 km/s (F) be capable of thriving not just in Eden's chemical environment but in early Earth's too, which would likely be quite different.
That's a lot of "try-try steps." It seems far more plausible to me that, if we have panspermia siblings, it's because of technological aliens deliberately seeding Earth.
Worth talking about directed panspermia (and whether or not it’s a good idea for us to do something similar with bacteria)