Recently there was a NASA press conference about finding that some life could tolerate arsenic and perhaps substitute it for phosphorus in some biochemicals. (There is a tiny bit of controversy of the method used to demonstrate that the arsenic was USED as opposed to just tolerated).
This has caused some folks to prattle on about other potential forms of life using other substitutions (me included, though only in a comment or two) including the staple of Sci-Fi: silicon based life.
What many folks may not realize is that life already uses silicon.
It’s not like it has to have whole new processes invented to absorb & utilize it.
So I thought I write a little article about the simple way it’s used, how we don’t know much about it, and that it’s largely in plants, like Bamboo, so herbivores will avoid the leaves. (One of the ‘issues’ in grazing stock and in my bunny ‘herd’ is that high silica plants wear the teeth too fast and somehow the herbivores know to avoid them. So I’ve a stand of tall timber bamboo, but few of the leaves are eaten, even when I present them to the bunnies.)
Nice idea for a simple and quick little article. But somehow these things never work out that way… Right off the bat, I run into a “scholarly article” that connects silicon to carbon utilization. So I’ll do that “simple bit” further down, but first we’re going to take a detour through diatoms…
Diatoms, Silicon and Carbon
From this article:
we have in the opening paragraph:
Diatoms are the world’s largest contributors to biosilicification and are one of the predominant contributors to global carbon fixation. Silicon is a major limiting nutrient for diatom growth and hence is a controlling factor in primary productivity. Because our understanding of cellular metabolism of silicon is limited, we are not fully knowledgeable about intracellular factors that may affect diatom productivity in the oceans.
Here we are smack up against all that “settled science” again. Predominant carbon fixer. Don’t know what controls its productivity. Understanding is limited. Silicon is limiting (and I wonder just how much work has been done on the “silicon cycle” to see how it controls the carbon cycle via diatoms… a google of ‘life “silicon cycle”‘ gave about 5700 articles and a lot of them are ‘misses’ where the terms are there but the topic is different. I think the diatom and silicate guys are missing out on the AGW Gravy Train here. Someone needs to send them the memo… ).
How important? Per the wiki “They are especially important in oceans, where they are estimated to contribute up to 45% of the total oceanic primary production.” So about half of what’s being made in the ocean. I’d say that matters. But wait, there’s more…
There is a battle between differing ocean critters over who gets to control the ‘silicon cycle’. This is thought to be related to the evolution of grasses (that also use silicon and, I presume, provide a more bio-available form of it in runoff to the oceans, but that’s just a guess). So given all that we’ve done to change the pattern of grasses on land and what lives in the oceans (think of all the various filter feeders AND things that prey on them which we’ve hauled out of the ocean and eaten to the point where they are at very low levels); do you think that could be doing something to the pattern of life in the ‘silicon cycle’ that could then impact carbon recycle? And what happens when Nature has a hissy fit and a load of volcanoes unload. They dump silicate ash in the oceans too… and have a big impact on things like sunlight.
What we don’t know here is huge.
Although the diatoms may have existed since the Triassic, the timing of their ascendancy and “take-over” of the silicon cycle is more recent. Prior to the Phanerozoic (before 544 Ma), it is believed that microbial or inorganic processes weakly regulated the ocean’s silicon cycle. Subsequently, the cycle appears dominated (and more strongly regulated) by the radiolarians and siliceous sponges, the former as zooplankton, the latter as sedentary filter feeders primarily on the continental shelves. Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms.
However, the precise timing of the “take-over” is unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves, suggests that this takeover began in the Cretaceous (146 Ma to 65 Ma), while evidence from radiolarians suggests “take-over” did not begin until the Cenozoic (65 Ma to present). The expansion of grassland biomes and the evolutionary radiation of grasses during the Miocene is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this has promoted the diatoms during the Cenozoic era. However, work on the variation of diatom diversity during the Cenozoic suggests instead that diatom success is decoupled from the evolution of grasses, and that diatoms were most diverse prior to the diversification of grasses. Nevertheless, regardless of the details of the “take-over” timing, it is clear that this most recent revolution has installed much tighter biological control over the biogeochemical cycle of silicon.
Ok, and we get to find out what “siliceous sponges” have been doing lately too if we want to understand the actual controls in the “carbon cycle” (via the silicon cycle controlling the diatoms as major primary production…)
In this article:
Dr. Roy W. Spencer lays out that C13 and C12 both vary with the same profile over the seasonal changes, so the change in the C12 / c13 ratio is a residual of that process. So he thinks the oceans could control CO2 levels.
I would add that since many plants have a different preference for one isotope over the other, changes in their rate of production and destruction can also influence the C12 C13 ratio directly. And we’ve done a lot of producing and destroying. So exactly what ARE the diatom levels in the ocean and what HAVE they done over the last 100 years as agricultural wastes have run into the ocean all over the planet? And how has that impacted CO2 levels and C12 C13 ratios? Then after you answer that, tell me what trawling has done to the siliceous sponges …
From the “slide show” here: http://www.geo.wvu.edu/~kammer/g231/MassExtinctions.pdf
we have a slide about the C12 C13 ratio that shows a great dilution of the C13 and notes
Dilution of C13 in biosphere carbon reservoir by rapid influx of C12 caused by methane release and mass dying at the end of the Permian. Organisms concentrate C12, which is released when they die.
Has the great dying of masses of life that the conservationists constantly wail about resulted in their C12 being “released when they die” and diluting things? And how do the diatoms figure into all of this?
So has the NATURAL warming of the planet increased the methane release from shallow clathrates such that a natural process could be diluting the C12 / C13 ratio? We don’t know as we don’t monitor the ocean bottoms.
All completely speculative, of course, … or IS it?…
From this link:
A decrease of the C13/C12 isotope ratio of 10 PPT has been found from end-Permian carbonate rocks around the world. This was the first and largest and most rapid of a series of changes of the isotope ratio that continued to occur until the Middle Triassic, when the ratio stabilised abruptly. It was only after the stabilisation of the C13/C12 ratio that organisms that form calcium carbonate structures like shells began to recover from the extinction event.
Oh. So we’ve had the ratio change before SUVs…. It’s a natural event and happens without us. Who knew?…
A similar situation to that during the closing Permian might be happening at the present. Scientists have been recording rising temperatures in the Arctic for some time. In 2008 a Russian research expedition vessel was measuring dissolved methane levels in the Arctic Ocean when they observed large patches of ocean where methane was bubbling to the surface along the north coast of Siberia. A British expedition also observed this phenomena in the seas closer to Britain. This indicates that the submarine permafrost is melting as well as the terrestrial permafrost, both of which are adding large amounts of methane to the atmosphere. Because of the low temperature of Arctic Ocean water the deposits of methane hydrates exist much closer to the surface of the ocean floor than they are elsewhere, where they can be several thousand metres below the sea bed.
On land melting permafrost has led to Arctic lakes, as in Siberia, becoming much larger, and with methane bubbling out of them.
So a load of old dead life from permafrost and old methane from under the arctic can be released / is being released, and all just from our present NATURAL warming cycle that’s been in place for several hundred years out of the bottom of the Little Ice Age and 1500 years before that in the Migration Era Pessimum / Dark Ages Cold Period when there was ice at Constantinople.
And now I’m left wondering what that has done to the diatoms and if they might be “contributing” anything?
In a couple of hours of search I was not able to find what the preferences were for C12 vs C13 in diatoms. This may be because I had poor choice of search terms or it may be because it changes:
The photosynthetic fractionation of carbon isotopes by blue-green algae in laboratory culture is dependent in a non-linear fashion on the CO2 concentration in the feed gas. For the three species tested, the minimum fractionation occurred at a CO2 concentration of 0.2% in air and was approximately zero for the two marine species tested. Enrichment of C12 in the reduced carbon is not an inevitable result of photosynthetic carbon fixation. Temperature and pH had no detectable effect on fractionation. The maximum fractionation observed in the laboratory cultures or in recent blue-green algal mats was 18‰. Differences in the isotope ratio of coexisting oxidized and reduced carbon in Precambrian stromatolites are as great as 31‰. Present carbon isotopic evidence is not consistent with the idea that blue-green algae were major contributors to the organic matter in Precambrian sediments.
So now I get to go study “blue-green aglae” for a year or three… Maybe I can talk some Algae Specialist into getting a grant to study C12 / C13 ratios in algae fixation and it’s relationship to Global Warming and hiring me as a lab rat….
Meanwhile, back at the CO2…
Now I found this rather startling. It says that at 0.2% CO2 there is almost no fractionation in one species and it varies with changed concentration of CO2. One species had an 18% concentration observed. So, as different species flourish, we get differential impacts on the C12 / C13 ratio. (Or so it looks from the abstract. Being behind a paywall I could not check this against the details in the article.) And one is left to wonder if diatoms have the same differential fractionation with concentration. AND as the concentration in the air changes, the fixation fractionation changes. Gee, wonder if that might impact the C13 / C12 ratio…
OK, enough down that path. It’s “ploughed enough” for others to know it’s got a big “Dig Here!” sign on the C12 / C13 ratio question. Now we can get back to silicon life… Though in abbreviated form. I’ll need to push most of that into some future article.
Oddly, an article about making pulp for paper and pulp products has an instructive chart about the relative presence of silicon in different plants. From:
we find this chart:
Species SiO2% Pine trace Birch trace Bagasse 1.5-2% Kenaf 3-4% Bamboo 1.5-2%
It clearly shows how silicon usage is highest in the grasses and nearly none in the trees. This matters for things like Giraffes in the zoos as folks often feed them grass hay when they naturally eat “browse” from trees in the wild:
Tooth wear in captive giraffes (Giraffa camelopardalis): mesowear analysis classifies free-ranging specimens as browsers but captive ones as grazers.
Clauss M, Franz-Odendaal TA, Brasch J, Castell JC, Kaiser T.
Division of Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland. firstname.lastname@example.org
Captive giraffe (Giraffa camelopardalis) mostly do not attain the longevity possible for this species and frequently have problems associated with low energy intake and fat storage mobilization. Abnormal tooth wear has been among the causes suggested as an underlying problem. This study utilizes a tooth wear scoring method (“mesowear”) primarily used in paleobiology. This scoring method was applied to museum specimens of free-ranging (n=20) and captive (n=41) giraffes. The scoring system allows for the differentiation between attrition–(typical for browsers, as browse contains little abrasive silica) and abrasion–(typical for grazers, as grass contains abrasive silica) dominated tooth wear. The dental wear pattern of the free-ranging population is dominated by attrition, resembles that previously published for free-ranging giraffe, and clusters within browsing herbivores in comparative analysis. In contrast, the wear pattern of the captive population is dominated by abrasion and clusters among grazing herbivores in comparative analyses. A potential explanation for this difference in tooth wear is likely related to the content of abrasive elements in zoo diets. Silica content (measured as acid insoluble ash) is low in browse and alfalfa. However, grass hay and the majority of pelleted compound feeds contain higher amounts of silica. It can be speculated that the abnormal wear pattern in captivity compromises tooth function in captive giraffe, with deleterious long-term consequences.
So feed your Giraffe alfalfa, OK? (The things you learn growing up in farm country… I always loved it when alfalfa was being harvested. Alfalfa hay has a wonderful smell to it.)
Humans and Lab Rats
I’m going to quote from a site pushing “supplements”. But it looks like a decent article and it’s neither paywalled nor does it have the copy function broken (like the academic articles I found).
Silica: A Little Known Element Comes of Age
by Rick Wagner
Silica’s importance in overall optimal bodily function has been recognized for quite some time. As early as 1878, Louis Pasteur predicted that silica would be found to be an important therapeutic substance for many diseases and would play a significant role in human health and consequently nutrition.
During the 20th century, progress was made by pioneering researchers and scientists such as Carlisle, Butenandt, Iler, Bergna, Kervran, and Schwartz. Edith Carlisle’s work in the 70’s through the 90’s at the UCLA School of Public Health, perhaps more than any other, demonstrated the necessity of having silica in the body for proper growth and development. As a result of her research, we know that silica is absolutely essential for the body to create and maintain collagen. What was dramatically shown through Carlisle’s research was that when silica is withheld from normal nutrition, gross abnormalities develop and normal growth does not take place. While Carlisle’s work was done with chickens and mice, humans have also been experimenting with silica.
This more scholarly article abstract says:
The highest levels of silicon are found in the epidermis and it’s appendages and in connective tissues in general.
So make sure you eat your bamboo shoots and grasses…
The point behind all this?
We already HAVE silicon life. Just not silicon BASED life. It would not be a great leap to increase the use of silicon in biological systems and I could even see the potential of having enzyme systems that built silicone like protein like structures. All purely the stuff of Sci-Fi; but not much to prevent it. Given that grasses evolved about 6 million years ago and the history of diatoms above indicates that they started using silicon after the fact; perhaps were simply on the first rung of that particular evolutionary ladder…