“When you arise in the morning, think of what a precious privilege it is to be alive — to breathe, to think, to enjoy, to love.” -Marcus Aurelius
How old is life on Earth? If all you had to go on was the fossil record, you'd run into severe trouble once you went back more than one or two billion years, as all your rock would have metamorphosed, making examination and identification of fossils impossible. But recently, we've discovered another method: to measure the isotopic content of carbon deposits in ancient rock formations.
The carbon-12 to carbon-13 ratio is a surefire signature of life, and tells us that life on Earth goes back at least 4.1 billion years: 90% of the age of our planet. Could this be the hint we've needed to conclude that life on Earth actually predates the Earth itself?
It's not quite certain, but the beauty of science is we can always test it and find out!
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How do we know that _only_ biologic processes enrich C12 vs C13?
What sort of signature would differentiate an organic C12/C13 ratio vs some alternate scheme from geologic or other things.
Because we have no other method by which that process can happen.
If you think this is incorrect, feel free to investigate other methods and determine if they pertain.
Wow, I'm asking a serious question - one I am sure the folks doing that research have answered! I bet the reasoning is interesting. Not every question is a creationist picking nits.
@MobiusKlein #1 and Wow #2: MobiusKlein, you ask a good question. And unfortunately, Ethan overstated things in the intro here (the actual article is slightly more nuanced, but not sufficiently).
In fact, there *ARE* non-biological processes which fractionate isotopes (that is the technical term for what's going on). For the specific case of 12C/13C fractionation, there are "several" non-biological process which can produce this signature (see, for example, the news article in Science magazine, http://news.sciencemag.org/biology/2015/10/scientists-may-have-found-ea…), including iron-based catalysis of hydrocarbons from carbon monoxide (https://en.wikipedia.org/wiki/Fischer–Tropsch_process, although the Wiki article does not mention isotopic fractionation).
More: the authors themselves discuss non-biological processes in their article, http://www.pnas.org/content/early/2015/10/14/1517557112, which is (amazingly enough!) not behind a paywall. You can read it for yourself, and not rely on interpretations or simplifications.
Rosetta just found molecular oxygen on Churyumov–Gerasimenko... :)
Mobius, try asking a different question, then, one that doesn't just go "I can't be arsed to look, please feed me!". Because it's most often used by trollers JAQing off on the internet.
Something as simple as dropping the accusatory "how do we know", and doing something like "Are there any non-biological methods for this too?".
The latter version asks the question you want answered. The former asks a question you apparently DON'T want answered (since I DID answer THAT question). I answered about the method of knowledge.
Michael gave you the answer to the former, which is about what we know.
See the difference?
What amazes me is that at some point, a quantum soup of fields, spins, symmetries and probability amplitudes becomes alive. Where is this threshold??
Until we find it, the definition of life is just "we know when we see it"!
I can save you or anyone else some time and wondering. The earth itself is approximately 6,000 years old. Then take the 6.000 years or so and subtract 5 days and that's when man was created. Simple math.
"Where is this threshold??"
The same set of quantum soup spins, fields, symmatries and probability amplitudes becomes dead.
Where's the threshold between alive and dead, Carlos?
Ever eaten a sausage? Some of those cells were still alive when it was cooked.
Thanks @Michael Kelsey, I'll peep.
@Wow, perhaps back off the hair trigger?
That is some serious effort they did there, ensuring purity & all.
And there is still lots to do in this area:
"There are considerable limitations of basing any inference
regarding early Earth on a single zircon containing primary
carbonaceous inclusions. Instead, we see this contribution as
demonstrating the feasibility of perhaps the only approach that
could lead to establishing a Hadean carbon isotope record. "
Looking forward to the additional confirmations.
What advantage does the panspermia hypothesis have over a terrestrial origin of life for explaining abiogenesis?
@Michael Hutson #12: None whatsoever. In fact, if you read the words you wrote, you might even realize that panspermia does _not_ "explain abiogenesis". It presumes, in fact, that biological systems on Earth originated from biological systems elsewhere.
Panspermia is not an explanatory framework. It's merely a way to finesse away the problem in an unfalsifiable way.
"@Wow, perhaps back off the hair trigger?"
Perhaps you should reconsider your queries.
STOP asking a question you don't want answered, STOP crying about the one you asked being answered, START asking the question you ACTUALLY WANT TO KNOW.
You know, learn how to learn.
It's a useful thing that kids are supposed to be taught in school.
Oh, and blaming ME for answering the query you made in a way you didn't like doesn't hide the fact that you ignored the message of what you did wrong.
Indicating you will continue to do it wrong, and whine and bitch about anyone not intuiting what you "meant".
Tell you what, don't consider your questions more carefully, and I won't back off on the hair trigger, and we can both be right.
That's why you ignored the advice, right? So you would be right rather than wrong?
So you ignore my advice and I'll ignore yours. And we're both right.
Exactly what I would have said, Michael.
Panspermia only explains (if it actually NEEDS explaining is entirely up in the air) the speed at which life-like chemistry started on the earth.
So instead of ~million(s) of years to get to some recognisable biotic chemistry on the earth which was a hot ball of boiling rock before, you can have ~billion(s) of years in a diffuse collection of planetesimals that many would collect, boil and form planets, but those that don't become part of the planetary system would continue to process their carbon chemistry into something life-like, and some of which would fall on the planets, and some of that would suit that planet. At least at the time it fell.
Panspermia answers a question about the speed of carbon-chemistry to biotic chemistry changing, but we don't really know if it's necessary to explain.
It doesn't explain abiogenisis.
For the record, I did ask a question I was interested in!
And read the paper cited too, and quoted an interesting bit from it. And learned from the paper too.
Then why whine when I answered it?
I told you how we know.
Michael answered a different question.
You thanked him.
Ergo, you didn't want the question you asked answered. You wanted the one that Michael intuited you wanted answered and supplied one.
Funny old me, using evidence in front of everyone's face to draw a conclusion, and not just trusting to the claims made ex nihilo.
"The earth itself is approximately 6,000 years old. "
For large values of 6000....
Like about 750 thousand times longer...
Ethan spend so much effort in making readable and interesting articles so it is rare to note a sloppy point. But this time there is an unfortunate illustration choice that is worth pointing out to avoid mistakes.
The images illustrating "bits and pieces" are of the erroneous diamond inclusions that were later found to be saw, grind and polish material (done by diamonds, often with an organic signature due to ecoglite diamonds deriving from recycled organic sediments). The Bell et al paper mentions them. "The >3.8-Ga Jack Hills zircons contain abundant mineral inclusions, mostly of a granitic character (11). Abundant and intimately associated diamond and graphite (4% of each in the zircons investigated) were reported in previous studies (16, 17) but subsequently shown to be diamond polishing debris and epoxy that had lodged in cracks during sample preparation (18)."
That is why the authors sorted through 10k zircons, of which ~ 5 % were older than 3.8 Ga. A big point of the paper is that they found just 1 zircon with fully enclosed carbon, it was organic and the rate of < 0.2 % is far less than the diamond polish occurrence of 4 %.
It isn't a slam dunk though, the best they can do is to exclude competing theories - such as Fischer–Tropsch mechanisms as source - as unlikely. That is why they need more material to confirm the exclusion.
What is a slam dunk is that the putative evidence fits without tension into the scant early evidence. Valley has characterized ~5 k zircons older than 3.8 Ga, and he can tell that there were crust 4 Ga bp (almost as old as the 4.006 Ga Nuvvuagittuq rocks, I recently found O'Neil's prediction the best explanation for the data). Valley can also tell that there was a habitable, relatively low pressure ocean before 4.3 Ga. TimeTree now lists 3 references that concur the first knowable split between bacteria and archaea can be dated to before 4.2 Ga. And the deltaC13 of these zircons, which are better isolated than younger Akilia and Isua organics, is exactly the figure that the Calvin cycle of photosynthetic bacteria produce, and archaea lack. Hence it could verify the split date.
Having an ancestral carboxylation RuBisCo of the Calvin cycle at the time would explain much. It is today slow and oxygen sensitive, fixes ~ 10 CO2/s compared to average enzyme rates of 100-100 reactions/s, so is the most common protein on Earth. But the CO2 concentration at the time could have been 250 000 times as large (~ 400 ppm vs ~ 100 atm), and the RuBisCo reaction rate could have been larger. [I found a paper that claims the reaction rate respond to higher pressures, but no quantification outside the paywall.]
Personally I judge the new - still putative - data point making martian transpermia or stellar panspermia hypotheses more difficult.
- The Calvin cycle signature implies the late bombardment could not extinguish life, because seeing the exact same enzyme before and after would be evolutionary unlikely. That is a strike against martian panspermia correlated with any late bombardment.
- Related, modern cells still bear the CHNOPS + metal signature of Hadean Earth crust and ocean element ratios.
- The scant data places life against a phylogenetic tree with origin on Earth as per the TimeTree data. That is problematic for interstellar panspermia.
- The zircon data on the ocean shows an increase in Earth water content until it plateaus. That is consistent with a supply of impactors from a dispersing disk, the same that provided LREEs to the crust. And it is fairly consistent, given dating uncertainties, with the later impact lull ~ 4.4 - 4.1 Ga that Bottke sees on the Moon and on asteroids et cetera. Mars didn't see the Moon-forming impact and didn't have to start over collecting volatiles. But on the other hand it wasn't much of habitability until the early bombardment let off, which both Earth and Mars saw simultaneously. And martian transpermia (or vice versa) gets more unlikely as impact rates went down. Ultimately we need models for these events!
- The thermal range of heat stress proteins rises as you go back in time over the Archean into the Hadean to converge on 70 degC. That is the exact temperature you would predict from the hot vent theory of emergence. It would not be the temperature adaptation you expect of panspermia from mature worlds.
[References withheld to save time at posting. Ask if something is of interest!]
Oops, that was 4.406 Ga Nuvvuagittuq rocks. Actually there is a few hundred million years of gap, since Valley's oldest zircon JH4.4 has been meticulously redated from 4.404 to 4.378 Ga (IIRC). (They spent 6 years on the first dating, that crystal is truly "some piece of work"!) O.Neil and others that use the data point as early crust - its dead on average value fits perfectly with the later volatile scatter as plate tectonics gets going - thinks it was so young it had never been subducted, hence the lack or zircons.
@Mobius: "How do we know that _only_ biologic processes enrich C12 vs C13?
What sort of signature would differentiate an organic C12/C13 ratio vs some alternate scheme from geologic or other things."
Now that you have looked at the paper note that the main problem in my mind, the Fischer–Tropsch mechanisms that mimic the organic carbon isotope ranges more tightly than meteoritic carbon, is excluded on the count that it hasn't been seen to produce particulates.
Speaking of particulates, it isn't mentioned in the paper because it is besides their research. But I notice that both measured inclusions - and perhaps more that wasn't included in their analysis sliver but unless they are image artifacts can be seen in their Fig 1 - are of consistent size, and of a size consistent with prokaryote cells.
I don't know taphonomy of cells in sediments, but Schopf always used cell like inclusions as his (erroneous) criteria for life so possibly it is a viable analysis. It would be interesting to know if cell remains could retain their sizes as they undergo the sediment - subduction -melt - crystallization process! Maybe there is more data on early Earth waiting to be wrung out of such zircons.
I wasn't going to put yet another comment up, I'm hogging this thread, but going elsewhere I stumbled on a pertinent piece of news. Also, I was exceedingly sloppy:
- "there were crust 4 Ga bp" - there were crust 4.4 Ga bp
- "100-100 reactions/s" - 100 - 1000 reactions/s
- "250 000 times as large (~ 400 ppm vs ~ 100 atm)" - 25 000 times as large (~ 400 ppm vs ~ 10 atm) since 1 - 10 atm CO2 is the more modern values.
Re martian transpermia:
Bottke doesn't like the "cataclysm" version of the late bombardment which hinges on the putative non-contamination from younger craters in Apollo rocks, Cavosie doesn't like any of it since he can't find any shocked zircons at the time but much later, I don't like that the early bombardment gives the right amount of volatiles making an intensive late one putting that data into tension (and possibly putting the putative fossil find into tension too).
Here is a putative late bombardment killer that popped up in my feeds:
"If we factor in the probability that the outer planetary orbits are well-replicated, we find a probability of 1% or less that the orbital architectures of the inner and outer planets are simultaneously reproduced in the same system. These small probabilities raise the prospect that the giant planet instability occurred before the terrestrial planets had formed.
This scenario implies that the giant planet instability is not the source of the Late Heavy Bombardment and that terrestrial planet formation finished with the giant planets in their modern configuration."
[ http://astrobiology.com/2015/10/the-fragility-of-the-terrestrial-planet… ]
Oops: "I don’t like that the early bombardment gives the right amount of volatiles" - I don’t like that the early bombardment gives the right amount of volatiles at the right time. [When including Valley's ocean data.]