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.
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.
It's not that uncommon for stars like the sun to pass close enough to each other for their Oort clouds to exchange material (because the Oort cloud radius is quite large). Many Oort cloud objects have water and clay-like interiors that can host complex, prebiotic organic compounds.
Life-and-water-bearing Oort Cloud objects could be passed along in chains of stellar communication, eventually seeding planets with their water and organic compounds. There is isotope evidence that Earth's own water was at least partially seeded by bombardments of icy, extraplanetary objects after its initial accretion.
While we observe evidence of life existing in only a minuscule fraction of space, we observe evidence of it existing continuously for a large fraction of time (about 1/4 to 1/3 the age of the universe). This implies that once life arises (however rarely), it is "sticky" and hard to get rid of, which seems like a property it would need to have for panspermia to work.
Are you familiar with extremophilic bacterium Deinococcus radiodurans? They can survive vacuum and hard radiation. Perhaps something like them are the seeds that have spread life throughout the Milky Way.
"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." Or we haven't found traces of earlier simpler life _yet_. Given how rarely life this old is preserved, and how hard even preserved life can be to detect, why would that be surprising?
One more argument for panspermia is observation selection effect: worlds where panspermia is possible, have much larger number of civilizations, so we are more likely to be in such world and more likely to observe effective mechanisms for interstellar panspermia.
This, however, doesn't mean that each galaxy with panspermia has many civilizations - it still could be less than one civilization for panspermia event.
Apparently the latest thinking is that the white dwarf star Gliese710 “could now arrive in 1.29 million years, instead of the previously calculated 1.36 million years”
It’s still anyone’s guess what “arrive” may actually mean as to implications for the earth. Or even for our solar system.
Meanwhile, I assume Greta Thunberg has been advised.
Local Eden or Heliospermia or a Goldilocks relay - life in the solar system began on Mars or Venus before Earth - while earth was still inhospitable for life. Mars was smaller and cooled faster. Venus was closer to a cooler sun in the early days of the solar system and may have had a planet wide ocean as soon as 0.2Gyr after formation. When Earth was fertile for receiving life it arrived ready evolved from a local neighbor. How that local neighbor got complex life so quickly remains open as this only ups the time for local evolution by few hundred million years or maybe a billion years. This does not preclude panspermia but it opens the window for our solar system to be ripe to receive it. The window for a possible heliospermia closed when Mars dried up so too did a possible stream of life baring kick off rocks and when Venus's atmosphere got thick rocks couldn't escape its atmosphere. But that too would be the same of any Eden world. It may have a window of Eden. The source of life eventually drys up but also the sink for life has a window too. Venus or Mars caught it and relayed it to Earth when she was ready. Martian meteorites have been found on earth some young and some old but none with evidence of life. Mars and martian asteroids remain to be studied. Could this mean we have life on earth today because we have a wide Goldilocks window?
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)
It's not that uncommon for stars like the sun to pass close enough to each other for their Oort clouds to exchange material (because the Oort cloud radius is quite large). Many Oort cloud objects have water and clay-like interiors that can host complex, prebiotic organic compounds.
Life-and-water-bearing Oort Cloud objects could be passed along in chains of stellar communication, eventually seeding planets with their water and organic compounds. There is isotope evidence that Earth's own water was at least partially seeded by bombardments of icy, extraplanetary objects after its initial accretion.
While we observe evidence of life existing in only a minuscule fraction of space, we observe evidence of it existing continuously for a large fraction of time (about 1/4 to 1/3 the age of the universe). This implies that once life arises (however rarely), it is "sticky" and hard to get rid of, which seems like a property it would need to have for panspermia to work.
Are you familiar with extremophilic bacterium Deinococcus radiodurans? They can survive vacuum and hard radiation. Perhaps something like them are the seeds that have spread life throughout the Milky Way.
"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." Or we haven't found traces of earlier simpler life _yet_. Given how rarely life this old is preserved, and how hard even preserved life can be to detect, why would that be surprising?
One more argument for panspermia is observation selection effect: worlds where panspermia is possible, have much larger number of civilizations, so we are more likely to be in such world and more likely to observe effective mechanisms for interstellar panspermia.
This, however, doesn't mean that each galaxy with panspermia has many civilizations - it still could be less than one civilization for panspermia event.
Prof Hanson, have you ever viewed, or read Mr. Petrov?
This is NOT a sale, or promotion, just some math regarding Panspermia.
https://www.youtube.com/watch?v=K4Zghdqvxt4
Apparently the latest thinking is that the white dwarf star Gliese710 “could now arrive in 1.29 million years, instead of the previously calculated 1.36 million years”
It’s still anyone’s guess what “arrive” may actually mean as to implications for the earth. Or even for our solar system.
Meanwhile, I assume Greta Thunberg has been advised.
Local Eden or Heliospermia or a Goldilocks relay - life in the solar system began on Mars or Venus before Earth - while earth was still inhospitable for life. Mars was smaller and cooled faster. Venus was closer to a cooler sun in the early days of the solar system and may have had a planet wide ocean as soon as 0.2Gyr after formation. When Earth was fertile for receiving life it arrived ready evolved from a local neighbor. How that local neighbor got complex life so quickly remains open as this only ups the time for local evolution by few hundred million years or maybe a billion years. This does not preclude panspermia but it opens the window for our solar system to be ripe to receive it. The window for a possible heliospermia closed when Mars dried up so too did a possible stream of life baring kick off rocks and when Venus's atmosphere got thick rocks couldn't escape its atmosphere. But that too would be the same of any Eden world. It may have a window of Eden. The source of life eventually drys up but also the sink for life has a window too. Venus or Mars caught it and relayed it to Earth when she was ready. Martian meteorites have been found on earth some young and some old but none with evidence of life. Mars and martian asteroids remain to be studied. Could this mean we have life on earth today because we have a wide Goldilocks window?
Why would there be any Panspermia siblings co-eval with us in the same galaxy if what happened on Earth was a once-in-a-million-galaxies event?