Evolution -How many times did life begin on earth

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Main Question or Discussion Point

I get the impression that all life on earth, including extinct life, goes back to the same single common source.
Is this the general view? Or could life have started out independantly at different times and/or places. If so is there any evidence?

Tony
 

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  • #2
matthyaouw
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I read the other day that people think multiple beginning are unlikely, as once life already exists, it would most probably metabolise any free floating proteins/RNA that could be a precursor to more life before it gets chance to develop in to more complex forms
 
  • #3
ShawnD
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I read the other day that people think multiple beginning are unlikely, as once life already exists, it would most probably metabolise any free floating proteins/RNA that could be a precursor to more life before it gets chance to develop in to more complex forms
Wouldn't this idea assume that all free proteins are at the same spot? If they're on opposite ends of the earth, one can't metabolise the other.
 
  • #4
matthyaouw
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I guess the idea is only relevant once life has become global.
 
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It's a good theory though. Perhaps, once the first 'life' had evolve, it spread around the globe very quickly and adopted its position of dominance.

The reason I was wondering is: If we could show that life started more than once on Earth, it'd suggest that extra-terrestrial life is more likely.
 
  • #6
turbo
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If life began in the oceans, it could have spread around the world very rapidly (a few years is a blink of the eye on evolutionary time-scales) even before it managed to develop any motility.
 
  • #7
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It is possible that the evidence that it DID happen here may be staring us in the face. Perhaps mitochondria and chloroplasts were indepentently evolved lifeforms that started off as a type of parasite to the eukaryotes, but over time developed a symbiotic relationship which led to both the animal and plant kingdoms.
 
  • #8
chemisttree
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I read the other day that people think multiple beginning are unlikely, as once life already exists, it would most probably metabolise any free floating proteins/RNA that could be a precursor to more life before it gets chance to develop in to more complex forms
Are you serious? Do you think that just before ‘life’ began that proteins and RNA were just floating around waiting for something to do or for some organizing principle to incorporate them into more complex life forms? Perhaps you meant ‘amino acids’ and ‘nucleosides’. Nucleosides themselves are very complex compounds. The ribose alone (the R in RNA) has 3 chiral centers and 2 prochiral ones. One of these prochiral centers is converted into a chiral center when attached to the purine or pyrimidine base. Even more unlikely is the presence of nucleotides on top of it all. That phosphate group is fairly hydrolytically unstable after all.

I think it is extremely likely that life began at least several times and perhaps millions upon millions of times. These nascent lifeforms perished for any number of reasons. Think about it, what is the likelihood that the first time that ‘life’ began (this early lifeform has yet to be defined) that it was well adapted to the slightly different environment of the mudhole right next to it. To one several miles down the beach? What is the likelihood that this nascent lifeform was a globetrotting monster???

Believing that life began from a single attempt actually argues against evolution. Instead, that interpretation argues for an act of creation…. and lets not go there!
 
  • #9
matthyaouw
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Are you serious?
Thats the arguement as I heard it, though I'm probaly wrong about the exact molecules involved...
 
  • #10
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Hi Chemisttree,
wow some strongly expressed views :-) Good points though. I imagine that suddenly the conditions were just right, and the same chemical reaction giving rise to life happened simultaneously in a lot of places, and all these life-molecules were able to interact. But I'd consider that just one instance of a start of life.

Why is life based predominantly on right handed sugars? What's wrong with the mirror image?

Hi Matthyaouw,
I understand the point you're making regardless of the molecules.
Interestingly, I read what what you say between the lines as "maybe there were several independant 'starts of life' on earth, but all bar one were trampled down before they even got started". Would you agree with this?
 
  • #11
iansmith
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Matthyaouw is talking about the RNA world hypothesis. RNA is a molecule that is capable of catalyzing reaction such as enzymatic reaction and storing information.

During the RNA world, there were no cellular organization has we know it but live wasn't just free floating either. However, the molecules of life probably form some type of organized structure called supramolecular aggregates. These were structures that could easily exchange genetic information and had some similarities to the cellular structures that we know today. So any new information that would arise from random chemical not-associated with supramolecular aggregates could potential be integrate in the system. Also the supramolecular aggregates do not leave a Darwinian-like lineage.

Those supramolecular aggregates gave rise to the three cell type we know today and each event was likely independent. Each cell type had to pass the Darwinian threshold and became more organized and were able to leave a lineage. Bacteria were the first to pass the Darwinian threshold from the supramolecular aggregates and the archea and eucaryotes then followed.

I think another question that should be ask is when should we consider that life began.
 
  • #12
DaveC426913
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I read recently that at least one scientist is arguing that life may be around even today that didn't emanate from the same event as the rest of the biosphere. He proposes it's clinging to existence in the niches and that it has gone heretofore undetected because our tests for life (DNA) are blind to it.
 
  • #13
chemisttree
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Hi Chemisttree,
wow some strongly expressed views :-) Good points though. I imagine that suddenly the conditions were just right, and the same chemical reaction giving rise to life happened simultaneously in a lot of places, and all these life-molecules were able to interact. But I'd consider that just one instance of a start of life.
I see your point. In my experience I rarely get something sooo right the first time. I think it very unlikely that the first spark started the fire....
 
  • #14
chemisttree
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I read recently that at least one scientist is arguing that life may be around even today that didn't emanate from the same event as the rest of the biosphere. He proposes it's clinging to existence in the niches and that it has gone heretofore undetected because our tests for life (DNA) are blind to it.
Absolutely! RNA world might once have been, but it seems unlikely that even that simplification of the cellular processes we see today is simple enough to account for the earliest form of life. After all, ribozymes can behave as enzymes but what are their substrates? Other complex structures?

I imagine our current investigations into the beginning of life of being like some quest to understand the very first instance of timekeeping by humans. We have as our only understanding of timekeeping the workings of a fancy Rolex watch. Someone removes the mainspring and notices that it vibrates with a fundamental frequency and assumes that the earliest timekeeping device must have been based somehow on the vibration of coiled pieces of metal. Another removes the balance wheel and notices how like a pendulum it is. A new theory based on pendulums being the first instance of timekeeping is proposed. The Mainspring Vibratos constantly argue with the Pendulum Swingers as to whose theory is the correct one. Elsewhere, a child pushes a stick into the sand and notices that it casts a shadow that moves as the day wears on....
 
  • #15
baywax
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It's a good theory though. Perhaps, once the first 'life' had evolve, it spread around the globe very quickly and adopted its position of dominance.

The reason I was wondering is: If we could show that life started more than once on Earth, it'd suggest that extra-terrestrial life is more likely.
The idea that life transfered from another solar system or another planet in ours to earth is a good bet.

Viruses of many different types can withstand the environ of space and could easily have "infected" earth before any life had a chance to form terrestrially.

Once earth was infected by viruses they provided the basis for a more complex DNA, perhaps coupling with different strains of Vdna or Vrna and coming up with the first bacteria, algaes or slime molds.

There are reports of a find called 'megavirus' that resembles bacteria so much it was mistaken as such. Studying the evolution of viruses will probably lead to the discovery that "they came from outerspace!"
 
  • #16
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Perhaps some literature would help

AFAIK, there is no definitive answer to this question. But for those who do want more than the limited space of the discussion forums, perhaps some links to current, accessible literature would help?

L. E. Orgel. http://www.biology.buffalo.edu/courses/bio129/medler_lectures/visuals/" [Broken]. Trends in Biochemical Sciences, 23:491–
495, 1998.

E. G. Nisbet and N. H. Sleep. http://www.cook.rutgers.edu/~dbm/NesbitSleepNature2001.pdf" [Broken]. Nature, 409:1083–1091, Feb. 2001.
.

M. A. Line. http://mic.sgmjournals.org/cgi/reprint/148/1/21" [Broken]. Microbiology, 148:21–27, 2002.
.

Leach, I. W. M. Smith, and C. S. Cockell. "[URL [Broken] conditions for the emergence of life on the early
Earth[/I][/URL]. Phil. Trans. R. Soc. B, 361:1675–1679, 2006.

R. Shapiro. http://sciam.com/print_version.cfm?articleID=B7AABF35-E7F2-99DF-309B8CEF02B5C4D7". Scientific American, February 2007.


Some of the considered hypotheses are more fantastic than SF novels.
In some cases there is direct discussion of the "multiple origins" of life, for example in
P. C. W. Davies and C. Lineweaver. http://aca.mq.edu.au/PaulDavies/publications/papers/FindingSecondSample.pdf". Astrobiology, 5:154, 2005.

I hope this short list would help someone.
 
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  • #18
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The idea that life transfered from another solar system or another planet in ours to earth is a good bet.

Viruses of many different types can withstand the environ of space and could easily have "infected" earth before any life had a chance to form terrestrially.

Once earth was infected by viruses they provided the basis for a more complex DNA, perhaps coupling with different strains of Vdna or Vrna and coming up with the first bacteria, algaes or slime molds.

There are reports of a find called 'megavirus' that resembles bacteria so much it was mistaken as such. Studying the evolution of viruses will probably lead to the discovery that "they came from outerspace!"
According to Prof. Chandra Wickramasinghe, "dust" grains in the Galatic Disk are actually bacterial spores*. Prof. Wickramsinghe has shown that grains of Interstellar "dust" absorb ambient starlight (as it travels towards the Earth) as if they were hibernating bacterial spores. Prof. Wickramsinghe concludes that Interstellar "dust" is bacterial spores.
* TLC It Came from Outer Space (VHS)
In the Proto-Solar Nebula, from which the Solar System eventually formed (~4.7 billion years ago), asteroids & (especially) comets swept up the frozen bacterial spores, preserving Life from the maelstrom of planetary formation. For, the early Earth was wholly molten, and hence inhospitable, even to hardy bacteria. For about a billion years (until ~3.8 to 3.5 billion years ago), the planet was repeatedly bombarded by impactors. These kept depositing their cargos of frozen bacterial spores, and and the Earth cooled to hospitable conditions, they seeded the world with Life*.
* According to the aforecited episode, bacterial spores have been recovered and resuscitated from 3 million year old antarctic ice, and from the stomachs of amber-trapped bees from 40 million year ago. According to the Discovery Channel documentary Into the Unknown -- Life on Mars (TV), bacterial spores have been recovered and resuscitated from 250 million year old rocks from mines.
Prof. Wickramsinghe says that "the only reasons for not attributing the absorption spectrums to [frozen] bacteria are sociological". For Prof. Wickramsinghe, the whole Galaxy is replete w/ frozen bacterial spores. Stellar Winds blow the bacteria from star to star. The only real risk for bacterial spores is UV radiation, which would perhaps prevent bacterial spores from "impregnating" big, bright A/B/O-Class stars' systems (which produce "hard" radiation spectrums)*.
* Moreover, A/B/O-Class stars probably don't produce planetary systems. See: Carroll & Ostlie. Intro to Modern Astrophysics, pg. 891.
Prof. Wickramasinghe also holds that Earth is continually "re-infected" (my words) by space-born bacterial spores & viruses. He has attributed the 1918 Spanish Influenza Epidemic, and the recent SARS Epidemic, to space-born microbes*.
* History Channel Mega Disasters -- Alien Infection (YouTUBE). ()


APPENDIX 1:

The figure attached below shows that "the match between the spectrum for dried bacteria (solid line) and the ones from the interstellar grains (dots, triangles and squares) [is] nearly perfect"*.



APPENDIX 2:

This absorption feature is probably specific to our Milky Way Galaxy:
The 2175 Å absorption bump, a feature often ascribed to graphite grains and ubiquitous in the spectra of sightlines through the Galactic diffuse interstellar medium, is generally weak or non-existent for objects outside our Galaxy. Many active galaxies seem to have SMC [Small Magellanic Cloud]-type dust extinction, suggesting that the presence of the bump in our Galaxy may be exceptional*.
Most scholars seemingly attribute the absorption spectrum bump to graphite grains**.
* http://www.stsci.edu/~kgordon/papers/paper_18.html
** Carroll & Ostlie. Introduction to Modern Astrophysics, pg. 442



APPENDIX 3:

Others attribute the absorption to organic compounds:
An Astronomical 2175 Å Feature in Interplanetary Dust Particles

The 2175 angstrom extinction feature is the strongest (visible-ultraviolet) spectral signature of dust in the interstellar medium. Forty years after its discovery, the origin of the feature and the nature of the carrier(s) remain controversial. Using a transmission electron microscope, we detected a 5.7–electron volt (2175 angstrom) feature in interstellar grains embedded within interplanetary dust particles (IDPs). The carriers are organic carbon and amorphous silicates that are abundant in IDPs and in the interstellar medium. These multiple carriers may explain the enigmatic invariant central wavelength and variable bandwidth of the astronomical 2175 angstrom feature*.
It seems that all scientists accept that Carbon-based (Graphite) or Organic compounds account for their feature. Prof. Wickramsinghe says that the Organic compounds are actually frozen bacterial spores.



APPENDIX 4:

Doug C. B Whittet (Dust in the Galactic Environment) devotes an entire chapter (Ch.3) to "Dust in the Galaxy", although avoids to attributing the absorption feature "near 2200 angstroms" to Life. A partial preview of the book is available online at Google Books.
 

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  • #20
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"Dust" is, unambiguously, blow into Interstellar Space by stellar winds (even if you disagree that said "dust" is microbial spores):

Our solar system belongs to a galaxy of some 100 billion stars threaded with clouds of gas and dust, much of it the debris of previous generations of stars. “Dust” in this context simply means microscopic bits of water ice, iron and other solid substances that condensed in the cool outer layers of stars and were blown out into interstellar space.

http://www.sciam.com/article.cfm?id=the-genesis-of-planets
 
  • #21
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wikipedia said:
On the 24th May 2003 The Lancet published a letter from Wickramasinghe, jointly signed by Milton Wainwright and Jayant Narlikar, which suggested that SARS could be extraterrestrial. The letter is currently (December 2006) referenced on the Cardiff Astrobiology website. It includes this claim:

With respect to the SARS outbreak, a prima facie case for a possible space incidence can already be made...

A small amount of the culprit virus introduced into the stratosphere could make a first tentative fall out East of the great mountain range of the Himalayas, where the stratosphere is thinnest, followed by sporadic deposits in neighbouring areas.
Uh...
 
  • #22
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According to Prof. Chandra Wickramasinghe, "dust" grains in the Galatic Disk are actually bacterial spores*. Prof. Wickramsinghe has shown that grains of Interstellar "dust" absorb ambient starlight (as it travels towards the Earth) as if they were hibernating bacterial spores. Prof. Wickramsinghe concludes that Interstellar "dust" is bacterial spores.
Well that all sounds <ahem> ....inventive. :wink:

I wonder if he postulates how this bacteria evolved in outer space?

Given the perfect conditions on Earth for life to form and evolve, I wonder why so many seem intent on believing it came from space with no explanation as to where it originated?
 
  • #23
baywax
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Well that all sounds <ahem> ....inventive. :wink:

I wonder if he postulates how this bacteria evolved in outer space?

Given the perfect conditions on Earth for life to form and evolve, I wonder why so many seem intent on believing it came from space with no explanation as to where it originated?
Space is a big place. As far as this solar sytem goes, Mars experienced a major collision that took half of its crust off. If it had developed life... including bacteria and viruses that go dormant in poor conditions (like space) then all that material would have been ejected into space. If some of the bacterial and viral life on the rocks and in the soil of the ejection survived long enough to go dormant in space, we could see Mars as the source for some of this transfer.

This sort of reasoning has a lot of "ifs", mind you.

Dust absorption of "starlight" and other light, even if it matches the absorption rate of bacteria, is not proof that there is life in dust clouds in space.
 
  • #24
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Well that all sounds <ahem> ....inventive. :wink:

I wonder if he postulates how this bacteria evolved in outer space?

Given the perfect conditions on Earth for life to form and evolve, I wonder why so many seem intent on believing it came from space with no explanation as to where it originated?
Prof. Wickramasinghe's arguments are consistent w/ a unique origin of Life. However, that unique origin would be the Milky Way Galaxy, not our Solar System (see "Appendix 2" above).

At some point in the Milky Way's assembly history, some unique Biogenesis event happened, spewing microbes across the region, and embedding bacterial spores throughout the Interstellar Medium (ISM) in the disk of our galaxy. Since this "bacterial dust" is strewn throughout our Galaxy, and not concentrated in a single region, then surely the spores were seeded into the proto-Galactic mixture at some early stage of its assembly. Simulations seem to show* that big galaxies, like the Milky Way, assemble "from the bottom up", from many smaller globular star clusters, which gradually merge. These massive mergers mix & mingle the gases & stars of those attracting clusters. Thus, a single prolific Biogenesis event, in a single star cluster, perhaps ~10 billion years ago, could have "infected" the whole galactic gravity well.
* Discovery Channel Unfolding Universe (DVD) ; National Geographic Journey to the Edge of the Universe (TV)
At the same time, similar "dust" is not observed in other galaxies (above). This dates our Biogenesis event to some time after the gases, destined for the Milky Way, started gravitationally attracting, and thereby separating out from the background Inter-Galactic Medium (IGM).

CONCLUSION (?): Given the apparent rarity of these Biogenesis events in the Visible Universe, surely a single Biogenesis event, about ~10 billion years ago, in a single (relatively) small star cluster, then "contaminated" the whole proto-galactic gravity well of the Milky Way, during a massive merger w/ other such constituent star clusters.

Further, since the Andromeda Galaxy is ~2 million light years away, this Biogenesis event probably happened w/in ~1 million light years (to remain in the Milky Way's gravity well).
 

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