The Origins of Life

Great Debates
1

I just read an interesting book which makes a strong case that life on Earth originated from interstellar bacteria.

The argument went like this:

  1. Many of the most primitive forms of bacteria are “adapted” to survive hard radiation, vacuum, and extreme cold. Some forms can survive dormant for millions of years. Why would they have these adaptations is they weren’t useful?

  2. The occasional Large meteor impact throws chunks of planetary material into space, and this could serve as the distribution system for these bacteria, which by now are pretty much spread across the galaxy, seeding life. That this occurs, and there is in fact exchange of planetary material can be seen from the contoversial Mars meteorite. Depite the argument about the fossils, it’s pretty much agreed it came from Mars in just this manner.

  3. The most interesting point was that even if life on earth was not started this way, it’s extremely likely that the earth is seeding the galaxy in just this manner from the impact of previous meteorites.
    Is this how life on Earth got started?

2

It’s not impossible, Scylla. IIRC, scientists have found evidence that organic molecules like formaldehyde have formed in interstellar space.

The Coyote gnaws …
but he does not swallow.

3

This theory was originally advanced by Svante Arrhenius back around the turn of the (20th) century. It’s plausible, but lacks falsifiability for the nonce. (Until we get evidence of extraterrestrial life, you can’t say what happened where.)

4

I have never seen panspermia as a very useful hypothesis. At present it is impossible to falsify it, and at best it just puts the abiogenesis “event” one or two iterations away from the only observed biosphere in the Universe.

From what I can see, I find it hard to accept that bacteria adapted to living in interstellar space could survive and thrive in the wet, hot environment at the bottom of this gravity well…

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
“The idle mind is the Devil’s playground.” -Professor Harold Hill

5

My understanding was that these bacteria wouldn’t thrive in interstellar space, they merely survive, dormant until they encounter favorable conditions.

I primarily find the theory interesting, because it suggests a profusion DNA based life throughout the galaxy.

It might also suggest that there could be bacterial life on Mars with terrestrial origins. Perhaps something like the bacteria that live inside the surface of rocks in Antarctica.

6

Scylla, just out of curiosity - what book did you read?

The origins of life is a very hot topic in biology & geology right now, partly because there’s just a fundamental interest in trying to understand how life developed on this planet, and partly because there’s a strong interest in trying to figure out what conditions may have permitted life to evolve on other worlds. (Yes, NASA is heavily involved in funding this research [check out their astrobiology website]; the National Science Foundation kicks in most of the rest of the $$$.) Current research into the issue involves a bunch of different disciplines and approaches, including the study of life in modern extreme environments (e.g., Yellowstone hot springs), geochemical evidence for biological activity early in Earth’s history (fossil biomarkers), and biochemical models & experiments.

The hypothesis you mentioned, also called panspermia, is certainly intriguing; it isn’t hard to imagine that extremophile organisms like Deinococcus radiodurans (which can withstand up to 15,000X the amount of radiation a human can, IIRC) evolved to survive life in the hard vacuum of space rather than life here in Earth. There are some complications, though, that will make it hard to demonstrate that this hypothesis is actually the right one. We have to get our hands on a life form that is clearly not of this Earth, but a) how can we be so sure that whatever probe we send to another world (Mars, Europa, Titan) won’t be carrying any sort of microbial contaminant that would confuse the sampling process, and b) if life on this planet had a common origin with life elsewhere in the solar system, the organisms’ biochemistry ought to be relatively similar, so we still wouldn’t be able to resolve the question of whether life began elsewhere and arrived here later, or vice versa.

Hypotheses for home-grown origins of life have gotten a bit more sophisticated than the “primordial soup” scenario originally developed by Urey and Miller in the 1950’s (i.e., lightning strikes through a primitive atmosphere with ammonia & methane to produce simple organic compounds that eventually link up to form living molecules), but for the moment these are equally speculative. Alternate possibilities include clays or iron sulfide minerals as substrates for organic molecule formation. To try to get a better handle on things, some scientists are conducting lab experiments to examine these ideas, while others are looking at life in hot extreme environments such as deep-ocean hydrothermal vents (“black smokers”), while others hope to explore cold extreme environments such as Lake Vostok in Antarctica.

Now, one of the real challenges is actually determining at what point a series of chemical reactions begins to display the characteristics of a living thing, i.e., the ability to replicate and the ability to undergo gradual change (evolve). That’s an additional debate that’s largely being addressed by biochemists (was early life an RNA molecule, a protein, an enzyme, etc.).

Like a lot of great science mysteries, we may never be able to reach a firm conclusion about what happened, but we’ll have a fascinating time trying anyway!

7

The book is Entering Space by Dr. Robert Zubrin. It devotes a chapter or so to this subject.

8

Just out of curiosity, how do these bacteria survive atmospheric entry? Are they supposed to be encased in the middle of solid rock?

9

Also, let’s calculate the odds against the extremophiles being in just the right rocks to be knocked off a planet by an impact. Unless they infest planets before the surface cools, I think it unlikely in the extreme.

10

The other I problem I thought of was interstellar travel time and the probabilities of catching the right planet rather than the more likely star or gas giant, but this seems less of a problem than atmospheric entry.

11

I don’t think it really matters if life began on another planet and then migrated here. As DrF so wisely put it, the abiogenesis event still must occur somewhere, so you might as well postulate the only living planet we know of, earth. The chemical reactions that led to the origin of life would be similar, regardless of their location.

12

A couple of interesting points:

  1. Live bacteria of Terrestrial origin were recovered from Surveyor spacecraft cameras left on the moon.

  2. “Evolution frequently preserves unnecesary adaptations, but it never goes out of it’s way to create them. If bacteria originated in the clement ponds and oceans of earth, why are they adapted to survive the hard vacuum, the radiation, the temperature extremes, and the extended periods of dormancy (230 million years in some cases) of interstellar flight?”

  3. Bacteria are everywhere on earth. Large impacts such as the dinosaur killer hurtle millions of tons of debris into space. It is logical to assume that some of that debris contained bacteria, and that some of it survived dormant.

  4. Reentry is survivable by microspic particles that do not have enough mass to penetrate the atmosphere with enough velocity to cause the friction to burn them up.

  5. Reentry may not be an issue. The bacteria may land on planets without atmosphere, and later actually create it!

  6. If the genesis of life on Earth did not occur in such a manner, Panspermia is almost certainly occuring now as debris from earth are being spread by the solar wind out of the solar system, and have been for the past 3.8 billion years!

  7. Life on earth occured almost as exactly as soon as the Earth was able to support it. The first bacteria appeared 3.8 billion years ago, almost as soon as the earth cooled. How did they appear on the scene so quickly? During the frequent bombardments ravaging the Earth, the ability to lie dormant, survive space, and propagate upon return (if they by chance reencountered the earth) would have been a strong survival mechanism, which would have favored those bacteria.

  8. If the solar wind propelled bacteria as it almost certainly did at a speed of 30km/s (the earth’s speed around the Sun,) than Bacteria from the Dinosaur killer (not to mention bacteria from other meteorites over the 3.5 billion years before the dinosaur killer) have had more than enough time to permeate the entire galaxy.

  9. There is evidence that meteoric impacts occured with greater frequency in the distant past. It seems logical that the first bacteria to survive and spread would be so adapted to space. After all, every atom of every element heavier than hydrogen on Earth originated in a star, long before Earth’s birth.

Panspermia may be an unsatisfying theory into the origin of life on Earth. The natural question is where did those bacteria originate? The point may be moot, because it speaks volumes for the possible existence of life on other planets. If life did not arrive in this manner, than the Earth has almost surely seeded the galaxy with bacteria from its biosphere. Makes it worth checking out Mars, Europa and other likely candidates.

Interesting, yet as others have mentioned unproveable aat this time.

13

As for being in the right rocks before the surface cools, I don’t think they need that. Sedimentary rocks might do just fine. Or, just the general surface material as it gets blasted into space from a meteorite.

Soembody’s got to stick up for these foolish ideas. I may be just that fool.

Often wrong… NEVER in doubt

14

Even if said particle isn’t large enough to burn up in the atmosphere, wouldn’t it be, in effect, sand-blasted by its high speed entry, and therefore wiped clean on the surface?

Can we say with any certainty when Earth’s atmosphere formed vs. when the surface was no longer molten?

15

Elephants can stand on their heads. This does not mean that they ever do such a thing outside of artificial circumstances, nor does it imply that evolution shaped them for head-standing behaviours in the unlikely event that circuses arise.

16

I would guess that the flat hard head of the elephant exists as an aid to pushing down trees. The head balancing seems a coincidence, and doesn’t seem like a specific adaptation.

The ability to survive a vacuum, radiation, temperature extremes, and dormancy periods of hundreds of millions a year, are all considerably more specific than head-standing.

Let’s say you found a fossil. This fossil is of an animal. It has fins. It has a blowhole on top of it’s head. It is streamlined. It has small sharp teeth suitable for snagging fish. It’s fins/legs seem incapable of propelling it on land.

Even if you had never seen a dolphin, you might reasonable guess that this animal lived in water.

If it says “Faaa loves paaa” or does flips for fish, how does that have anything to do with it? It is the same with the elephant.

Often wrong… NEVER in doubt

17

mrblue:

I have no idea about the sandblasting. Maybe 99.999% of the bacteria would die this way. If .001 are lucky enough to survive, then maybe that’s enough.

18

Dr. F.: Thanks! Best analogy against the Anthropic Principle I’ve seen in a coon’s age. :slight_smile:

19

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.

  2. Culture a bacteria from the samples of moondust we have retrieved or from any interstellar dust collected in orbit. A measurable proportion of interplanetary dust should be bacteria spores if the theory is valid.

Failing either of these two tests (or something else that I have not thought of yet [I am open to any reasonable suggestion]), I would say that panspermia does not pass Ockham’s scalpel. It is fun to blue-sky speculations, but there needs to be evidence for a proposition for it to be useful.

Dr. Fidelius, Charlatan
Associate Curator Anomalous Paleontology, Miskatonic University
“The idle mind is the Devil’s playground.” -Professor Harold Hill

20

For test #1

Streptococcus Mitis colonies produce a protective coating when the outside layer of bacteria are exposed to any of these conditions. This protective coating is of course the dead outer layer. They even go sar far as to release Glycol which stops the rupturing of subsequent layers and facilitates a freeze drying process.

Many, many bacteria produce endospores which are quite capable of surviving all these conditions.

Halothermophilic Archaea bacteria, can do all these things, and are pretty good examples of extremely ancient bacteria.

My bacterial researches of an earlier thread yielded some fruit here.

Of course this proves nothing until a colony of bacteria is generated from uncontaminated extraterrestrial material. Even then it would just show that Panspermia is working from the Earth outwards, not vice-versa.

Positing 10 billion plus years in which to work, Panspermia seems viable.

Another question to ask is how difficult is it for life to arise?

If it’s rather than the occurence of Panspermia may be incidental to life arising indepedently on Earth or elsewhere.

If it’s difficult, than the fact that life arrived so quickly on Earth 3.8 Billion years ago) is an argument in its favor.

How many hundreds of millions of years does it take for a bacteria to spontaneously evolve from the primordial soup?