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View Full Version : Radioactive Hot Spots on Earth's Beaches May Have Sparked Life



Fraser
2008-Jan-12, 11:40 PM
We've heard about life being created in a puddle of primordial chemical soup, sparked by lightning strikes, or organic molecules falling to Earth from comets or planets, such as Mars. But now, there is an alternative. Early Earth was radioactive; the Moon also had a lower orbit, generating strong tidal forces. Due to the close [...]

More... (http://feeds.feedburner.com/~r/universetoday/pYdq/~3/215700210/)

neilzero
2008-Jan-13, 12:21 PM
That seems reasonable except the tides caused by the large very close moon separating/concentrating chemicals such as uranium. Does this occur even very slightly today in places such as the Bay of Funday which has very high tides? Perhaps it does, as I understand titanium oxide is found in rich depostits in beach sand in a very few locations. Neil

Trakar
2008-Jan-13, 04:29 PM
That seems reasonable except the tides caused by the large very close moon separating/concentrating chemicals such as uranium. Does this occur even very slightly today in places such as the Bay of Funday which has very high tides? Perhaps it does, as I understand titanium oxide is found in rich depostits in beach sand in a very few locations. Neil

Well, we can see perhaps a modern equivilant in beach gold. I do some prospecting as a hobby and I could see large regular tides acting as a mixing and sorting agent, but any U present wouldn't be alone, and most of the heavier agents associated with such (predominantly gold, iron, lead) would tend to moderate or dampen any "natural" reactor formation. I just don't see it as very plausible in mechanism of formation. The natural reactors of which we are aware (http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml), formed from different processes.

JonClarke
2008-Jan-14, 06:58 AM
Well, we can see perhaps a modern equivilant in beach gold. I do some prospecting as a hobby and I could see large regular tides acting as a mixing and sorting agent, but any U present wouldn't be alone, and most of the heavier agents associated with such (predominantly gold, iron, lead) would tend to moderate or dampen any "natural" reactor formation. I just don't see it as very plausible in mechanism of formation. The natural reactors of which we are aware (http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml), formed from different processes.

Hydraulic sorting and segregate minerals very efficiently according to density, and high grade uranium-bearing sands are not impossible in a reducing environment. It would be interesting to moddel and see whether you could get a sufficient concentration to generate a nuclear reaction, given historic isotope ratios.

Jon

Trakar
2008-Jan-18, 05:33 PM
Hydraulic sorting and segregate minerals very efficiently according to density, and high grade uranium-bearing sands are not impossible in a reducing environment. It would be interesting to moddel and see whether you could get a sufficient concentration to generate a nuclear reaction, given historic isotope ratios.

Jon

You bring up an interesting point I wasn't considering in my earlier post. We are talking about several Billion (million million, for some) years ago, not only would U have been much more plentiful, but the isotopic compositions of such would probably have been quite different as well. This would indeed affect the viability of such a "natural reactor" proposal as it would generally mean much lower concentrations of raw ore would tend to be more reactive. I'm still hesitant to endorse such as probable, but it does seem potentially possible.

As we actually seem to have numerous sources for the energy which stimulated the emergence of abiogenesis, and radiation tends to be more inimical than beneficial to the compounds we are currently looking at as potential precursors, I don't really see this as positive step in that process. Seems more like an unlikely, but potential, solution in search of a problem, at least at this point.

JonClarke
2008-Jan-19, 01:45 AM
You bring up an interesting point I wasn't considering in my earlier post. We are talking about several Billion (million million, for some) years ago, not only would U have been much more plentiful, but the isotopic compositions of such would probably have been quite different as well. This would indeed affect the viability of such a "natural reactor" proposal as it would generally mean much lower concentrations of raw ore would tend to be more reactive. I'm still hesitant to endorse such as probable, but it does seem potentially possible.

thi is why you could get natural reactors at Oklo, because the isotopic ratio was equivalent to slightly enriched nuclear fuel, and why such phenomena are impossible today.


As we actually seem to have numerous sources for the energy which stimulated the emergence of abiogenesis, and radiation tends to be more inimical than beneficial to the compounds we are currently looking at as potential precursors, I don't really see this as positive step in that process. Seems more like an unlikely, but potential, solution in search of a problem, at least at this point.

Some prebiotic synthesis has been demonstrated using X-rays, proton beams, and alpha particles.

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APPLAB000074000006000877000001&idtype=cvips&gifs=yes

http://www.springerlink.com/content/qwh6828826357788/

Trakar
2008-Jan-19, 03:51 AM
thi is why you could get natural reactors at Oklo, because the isotopic ratio was equivalent to slightly enriched nuclear fuel, and why such phenomena are impossible today.

actually, a bit more than just "slightly" enriched, which was my original impression. around 2million years ago which is the approximate age of most of the natural reactors known ore enrichment was at around 3.7% U235, which as you say is slightly enriched. But drop that figure back another nearly 2 billion years at around the time of abiogenesis, and we're pushing up closer to 7%, which is a pretty potent fuel mix. Most modern reactors use fuel at between 3.5 - 5%, IIRC.


Some prebiotic synthesis has been demonstrated using X-rays, proton beams, and alpha particles.

http://scitation.aip.org/getabs/servlet/GetabsServlet?.prog=normal&id=APPLAB000074000006000877000001&idtype=cvips&gifs=yes



http://www.springerlink.com/content/qwh6828826357788/


I wasn't aware that these specific energies and radiations were being proposed as plentiful and typical of these types of reactors/reactions,....but if you are just saying, that we don't know what we don't know and that this creates similar processes and may produce unknown similar prebiotic percursors, ...yeah, anything's possible, I just don't see any strong compelling evidence of it yet.

Many other more common processes precursors that may have yielded abiogenesis. I'm not trying to slam any doors, just doing a bit of shaving until presented with a reason for what so far seems an unneccesary complication.

How about this for a leap to the side, however, what's a heavy element like Uranium doing in our planet's crust anyway? :)

JonClarke
2008-Jan-19, 05:13 AM
actually, a bit more than just "slightly" enriched, which was my original impression. around 2million years ago which is the approximate age of most of the natural reactors known ore enrichment was at around 3.7% U235, which as you say is slightly enriched. But drop that figure back another nearly 2 billion years at around the time of abiogenesis, and we're pushing up closer to 7%, which is a pretty potent fuel mix. Most modern reactors use fuel at between 3.5 - 5%, IIRC.


That's a good point. Thanks for the calculation.


[QUOTE=Trakar;1155186]I wasn't aware that these specific energies and radiations were being proposed as plentiful and typical of these types of reactors/reactions,....but if you are just saying, that we don't know what we don't know and that this creates similar processes and may produce unknown similar prebiotic percursors, ...yeah, anything's possible, I just don't see any strong compelling evidence of it yet.

Many other more common processes precursors that may have yielded abiogenesis. I'm not trying to slam any doors, just doing a bit of shaving until presented with a reason for what so far seems an unneccesary complication.

It's not a complication, so much as an additional "factory" for making complex prebiotic compounds. The more the better to improve the quality of the soup.


How about this for a leap to the side, however, what's a heavy element like Uranium doing in our planet's crust anyway? :)

Uranium is a lithophile element and so is concentrated in fractionated crustal rocks. Under reducing conditions uranium is insoluble and will therefore be further concentrated as a detrital mineral in sediments.

Trakar
2008-Jan-19, 08:06 AM
[QUOTE=Trakar;1155186]Uranium is a lithophile element and so is concentrated in fractionated crustal rocks. Under reducing conditions uranium is insoluble and will therefore be further concentrated as a detrital mineral in sediments.

But, if not for unusual circumstances, shouldn't we expect that like the vast majority of iron and other heavy metals, it should have been differentiated and sought levels more appropriately in the core/deep mantle?

Just a casual look and consideration seems to present that the Earth possesses a lot more of the heavier metals in its crust than I would expect from the accretion and differentiation phases of planetary formation.
Even granting the lithophilic nature, we are still talking average specific gravity for most U minerals in the 7.5 to almost 10 range, I believe. Are there other obvious processes that I'm overlooking? I mean, I understand that there is never perfect differentiation, and once the core forms it tends to remain distinct from the mantle and the crust, and all you have to do is look at Mars to see that heavier elements like iron are not all that uncommon on the surface of planets (though Mars looks like it had a few big late period impacts itself - Tharsis Bulge, etc.). But we seem to have a lot of heavy metal ores that seem a bit out of place in our planet's crust, even given the nature of mantle circulation and plume upwellings. Any recommended reading material that covers this topic in more detail would be greatly appreciated.

Trakar
2008-Jan-19, 08:22 AM
actually, a bit more than just "slightly" enriched, which was my original impression. around 2million years ago which is the approximate age of most of the natural reactors known ore enrichment was at around 3.7% U235, which as you say is slightly enriched. But drop that figure back another nearly 2 billion years at around the time of abiogenesis, and we're pushing up closer to 7%, which is a pretty potent fuel mix. Most modern reactors use fuel at between 3.5 - 5%, IIRC.



That's a good point. Thanks for the calculation.

Actually couple corrections there. Most of the natural reactors were around 1.8 "B"illion years ago and U235 was about 3.7% of the U ore then, and if we stretched it back to life originations at around 4 "B"illion the ratio of U235 to U238 is almost 1-2 or much closer to 30%! Not weapons grade, but definitely some hot fuel. Good catch and thanks for calling my attention to it, looking at it in your post, I realized it didn't look right but it took me a bit to see where I'd been sloppy. U235 half-life ~700Myears.

JonClarke
2008-Jan-19, 11:26 AM
[QUOTE=JonClarke;1155207]

But, if not for unusual circumstances, shouldn't we expect that like the vast majority of iron and other heavy metals, it should have been differentiated and sought levels more appropriately in the core/deep mantle?

Just a casual look and consideration seems to present that the Earth possesses a lot more of the heavier metals in its crust than I would expect from the accretion and differentiation phases of planetary formation.
Even granting the lithophilic nature, we are still talking average specific gravity for most U minerals in the 7.5 to almost 10 range, I believe. Are there other obvious processes that I'm overlooking? I mean, I understand that there is never perfect differentiation, and once the core forms it tends to remain distinct from the mantle and the crust, and all you have to do is look at Mars to see that heavier elements like iron are not all that uncommon on the surface of planets (though Mars looks like it had a few big late period impacts itself - Tharsis Bulge, etc.). But we seem to have a lot of heavy metal ores that seem a bit out of place in our planet's crust, even given the nature of mantle circulation and plume upwellings. Any recommended reading material that covers this topic in more detail would be greatly appreciated.


Where metals end up in the Earth (or any other planet for that matter) is not determined by density but by geochemical behaviour, as determined by Goldschmidt (see http://en.wikipedia.org/wiki/Goldschmidt_classification). Heavy metals can be lithophiles (rock loving), chalcophiles (literally copper loving but in practice they could be better described as sulphur loving) and siderophile (iron loving).

The lithophile elements include uranium and thorium, these tend fractionate into crustal rocks, the more fractionated the better. Siderophile elements partion into metallic iron, and tend to occur as alloys or native metals, gold and the PGEs for example. Chalcophiles tend to form sulphides, like bismuth, copper, lead, zinc, etc.

So during planetary differentiation U and Th will end up in the crust, metallic iron and the PGEs in the core, and copper, lead, zinc where ever there is sulphur, be that in the core, in igenous rocks, or hydrothermally concentrated in the crust.

The caveat is that the Goldschimdt classification indicates patterns of geochemical behaviour. Some elements, iron for instance, can behave as siderophiles, chalcophiles or lithophiles, depending on circumstances. Others are much more narrow in their beaviour. Uranium is one and is always lithophile. PGEs are another, and are always siderophile.

Jon