Primordial soup… This is WAY off topic, but I wonder if Campbell’s has ever tried marketing “Primordial soup” with little dinosaur noodles…
I would think that if it were difficult for chemistry to bootstrap itself up to “life” that would be a strong argument against panspermia.
Not only would there be astronomical odds against life arising anywhere, one would have to multiply those odds against the probability of that life being knocked into interstellar space and stumbling upon this planet.
If solar wind pushes the space-germs out of their original system, how do they overcome the solar wind pressure of their target system’s primary?
I may have missed this question being raised, but how would bacteria evolve the capabilities to survive literally hundreds of millions of years, allowing for the number of generations and ‘mass extinctions’ that cull the populations, when the universe itself is only about 12-15 billion years old? Am I correct in thinking this would only leave about 120-150 100-million-year cycles of growth/death/regeneration, with most of each cycle taken up by the bacteria in stasis?
Here’s my guesses.
If life just spontaneously arises everywhere, who cares about Panspermia? It need not be a factor.
Let’s just take a guess for a second and say the odds of life developing to the bacterial level on a given suitable world in 500 million years are one in 50 million. Let’s also guess that their are 2 billion suitable worlds in the galaxy. Let’s also pretend that Meteoric bombardment produces a dinosaur killer type asteroid once every 25 million years or so, and that this is a constant.
In the first 500 million years our one world produces bacteria. Let’s say it does so at year 250 million. It then gets whacked 10 times with big asteroids sending millions of tons of microbe containing debris into space.
Some of this stuff rides around on asteroids, other stuff is dispersed like mist on the solar wind.
In both circumstances, some of it escapes it’s solar system.
A fraction of this encounters another solar system. Maybe some sticks to a comet and rides that intothe inner solar system and gets disersed to the planets along the cometary tail. Others ride in on meteorites.
Depending on where you place the chances of a successful seeding of another planet in betweeen 25 million year meteor strikes (I would guess it to be high since a lot of stuff gets tossed up by meteors and would probably spread out pretty quickly,) you could argue that all two billion planets would be seeded by our first succesful life generating planet within a couple of billion years. (place the odds where you like and play with it.)
Given 10 billion years or so, even astronomical odds make it work decently.
There are similar mechanisms on Earth today.
Wind pollination, plankton just dumping sperm into the sea hoping it encounters the right egg, even the parachutes on Dandelions sending the seeds on a wind-driven journey for livable ground. Brine shrimp eggs getting blown across deserts, algae spores. etc. etc.
Nature makes it’s living with astronomical odds. Do it enough for long enough and it becomes a certainty.
Then again, I am…
Often wrong… NEVER in doubt
What are the odds of any given sperm ever fertilizing an egg?
Pretty astronomical.
I have evidence that this occasionally happens though. Me.
Some back-of-the-envelope figures:
Escape velocity from the solar system is about 600 kilometres per second.
The Earth’s orbital velocity is about 30km/s.
So, the hypothetical bacteria blasted into space as ejecta from a Chicxulub-level impact still need to be accelerated twenty-fold before they can hope to start a journey to another star.
The closest star is 38,000,000,000,000 km away (give or take). So our bacteria would need 120,500 years to reach Proxima Centauri, assuming that they are aimed exactly at that star. The nearest stars in the plane of the ecliptic (which is the most likely vector the ejecta could follow) are many times farther away.
I feel that anyone who advocates panspermia is ignoring the size of space and the unlikelyhood of any given life-bearing shard entering a system with a planet that can support life (as we know it). I am, of course, always open to new evidence. If we find that interplanetary dust has encysted bacteria in it, or if after we capture a comet we find bacteria, I will change my mind. Until such time I feel we have no reason to postulate panspermia.
In an earlier post Dr: Fidelius said:
Quote:
Okay, there are two ways to go here.
1) Show that there is at least one species or strain of bacteria which can survive all the
rigors of drifting through interstellar space. That is, we know that there are varieties
which can handle the cold, the heat, the vacuum, the radiation, and the longevity
problems. Find one that can do all that and show that it is similar to the ur-bacter,
rather than having those adaptations in response to extreme niches on Earth.
endquote:
I have provided you with three examples.
I forgot about the escape velocity from the solar system. This actually strengthens the case. The solar wind is well capable of acclerating dust motes to more than twice solar escape velocity.
The sun is basically radiating material away from the solar system.
If a fortuitous bacterial spore were able to catch a gravity assist from a nearby massive object, they could go even faster.
In support of this contention I cite: Carl Sagan Intelligent Life in the universe, Seth Shostak Sharing The Universe, and RH Zubrin and D. Andrews “Magnetic Sails and Interplanetary Travel” Journal of Spacecraft and Rockets April 1991
But let’s use your figure of 600km/sec. That takes 26,777 years for a bacterial spore to cover a light year. We know that spores can survive for 250 million years (maybe more), and provide viable cultures. Let’s call this the upper limit. That means a bacterial spore can travel 9,000 or so light years and remain viable.
It’s estimated that the milky way galaxy contains 300 billion stars, and it rotates about once every 250 million years. It’s 103,000 light years in diameter. That gives us 8.3 million square light years as the size of the galaxy through the plane of the ecliptic. It’s also about 5-10,000 light years thick. Take 7.5 as average. That gives us an average stellar denstity of about 1 star every two light years.
You cannot draw a line across the plane of the galactic ecliptic for 9,000 light years without encountering another star. In fact each bacterial spore traveling across the plane of the ecliptic should have the oportunity to pass within 1/2 light year of 1,000 different stars while it is still viable, and possibly be captured by one of those systems.
One out of ten stars is a type g or k, similar to our sun.
That’s 100 possible candidates.
Let’s arbitrarily decide that 1 out of ten suns is a solar system similar to ours, with small warm inner planets (best data right now says the odds are better than this.)
That’s ten possible candidates, or a 1 in one hundred chance for a given bacteria to end up in a viable solar system.
Let’s be arbitrary and say that only one in a million of these will ever find itself intact in a suitable place on a viable planet.
That means that 1 in 100 million bacteria pushed out of the solar system finds itself on another planet outside the solar sytem where it can thrive.
If you consider a Dinosaur killer throwing tens of thousands of tons of bacteria filled earthly matter containing hundreds of billions of bacteria(only a small portion of which ever survives the ordeal) up into space once every 25 million years or so for the last 3.8 billion years, that makes the odds of terrestrial bacteria thriving on another planet outside this solar system a statistical certainty.
It also means that statistically speaking, virtually every earthlike planet in the galaxy has encountered terrestrial bacteria.
Now the galaxy is probably about 5 billion years older than the Earth.
Reverse that equation. Assume that one planet originated life 7 billion years or so ago. Allowing for the spread of life in this fashion it is a virtual cetainty that Earth has been bombarded with these bacteria since its creation. It may not matter if life could spontaneously evolve on Earth. Bacterial spores would spread throughout the planet before native life vould gain a toehold.
Combine this with examples of space-adapted bacteria, and there is enough evidence that this theory deserves careful consideration.
It’s fun, but is it useful?
Well yes, it suggests a galaxy teeming with carbon/DNA based life. It suggests a likelihood of finding life on both Mars and Europa. It increases the argument for the infamous Mars meteorite actually showing fossil evidence of bacteria. It changes the way we look at life on earth, our understanding of evolution, and suggests areas of study in microbiology. It answers the question concerning how life evolved up to the bacterial level so quickly.
I find that useful, interesting, and well worth consideration. Fun too.
By the way, I was very careful with the above numbers, and erred towards conservatism if I erred.
This means Grampa was E.T.
DrFidelius
For the getting from here to there calc don’t you have to figure in the rotation of our galaxy also?
Trouts:
I left it out, because I assume any object thrown out of the solar system will maintain its velocity relative to the rest of the galaxy.
In the case of Dr. Fidelius’ trip to Proxima Centauri (and boy are his arms tired,) galactic rotation would not come into play for a relatively short trip of 125,000 years or so.
Maybe trouts. Do you happen to know the relative motions of Sol and the Centauris?
I am trying to digest the figures scylla used. I believe there is a touch of Olbers’ paradox there, but as I am a ragged and slow thinker it may take me a while to enunciate the problem.
God, I hope this Olber guy isn’t like Lamarck.
Nice job Scylla. I can’t do the math and just able to follow you.
DrFidelius, No. All I know is they are not all rotating at the same rates. For example, the arms are apparent and not real.
I’m trying to find a cite for the 250 million year survival estimate for bacteria. The oldest I can find is 135 million years, and those were recovered from a bee in amber. Which is a far more clement environment than interstellar space.
Does anyone have a figure for the amount of radiation something would encounter over a space flight of several hundred thousand to several million years?
For our purposes, I think we can assume that stars positions remain constant to one another, as the Centaurus spiral arm (which I think is the one we are on) tends to move as a whole.
Overrall galactic rotation would facilitate panspermia if we assume the bacterial spores don’t rotate with the galaxy and maintain relative positon. I don’t see why we should assume that.
I believe Olber’s paradox refers to the relative visibility of stars, and not their distribution. The Milky Way band of light visible across the night sky describes the predicted glow, while closer, brighter stars overshadow their dimmer cousins.
Admittedly I fudged the distribution of stars as uniform when in fact it is not. I did this to facilitate the math. What I am pursuing is an AVERAGE likelihood of a bacterial spore encountering a home. The odds would obviously be greater where stellar density is increased and vice-versa.
I got bacteria from Permian salts, 230 million years.
50,000 years in space gives you about a million rads. Some bacterial cultures can take about 10 million or so rads. I have no idea what spores can take.
That might be moot because a bacteria or spore on a couple of grains of dust would get some shielding.
I don’t know how to quantify that to get a realistic figure for a bacterial spore’s survival in space.
I don’t mean I HAVE bacteria, I found a cite.
Scylla’s calcs, which seem more or less in line (as far as I can tell) are fairly convincing, but I have to go with the doc. Panspermia still begs the question: If life did not originate here, how did it rise up in the first place? The idea that life came from somewhere else is very convenient in light of recent evidence that cuts the window down from several billion years to a few hundred million (Earth habitable 4.2 Ba, life at 3.8 Ba. And fairly complew life, relatively speaking). But I have not yet given up hope that life probably started here.
-dave
It’s not how you pick your nose, it’s where you put the boogers
Lastly, I see no reason why bacterial spores should be “naked” in space. Bacteria grow in clumps and would likely remain that way as they got catapulted into space. Any small amount of material (including “dead” bacteria) that they were encased in would provide some shielding.
Admittedly, a smaller clump would ride the solar wind at a faster speed, and have less long term survivability.
A large clump would go slower, but last longer.
The 600 km/ sec. figure seemed like as good an average as any. Get a gravity assist and a really small thin clump presenting the right profile, and you can choose 3000+ km/sec. I have a chart for that, From The Journal of The British Interplanetary Society. I decided not to go that high, because it seemed unlikely as the average.
Something that hitched a ride on a comet, asteroid, or encased in a microspic lump of dirt might be completly shielded, I don’t know.
The 250 million years is a guess. They might last much longer, or not.
Bigdaddy:
I don’t care if it started on Earth or Trafalmador. I just want to know, or failing that, have the best guess for its ownsake.
As I see it Panspermia may point towards the kind of universe we live in. The likelihood of life on other bodies within the solar system, or if we live in a “green galaxy” populated by our cosmic kin.
If the theory has any validity, and you have sex with an alien from Alpha Centauri, it could mean your committing incest!
These are the kind of things we just have to know.