Previous Fitness for Life: The Boron Problem

Photo credit: NPS, Patrick Taylor.

Boron is not an element often considered in lists of essential ingredients for life. It is not incorporated into any animal enzymes, fats, proteins or nucleic acids, and few of us look at the boron content on our food labels. The Arizona State University list doesn’t even include boron, which makes up a minute fraction of body weight. And yet, surprisingly, there would be no life without boron: no plants, no bones, no brains. Why do we need it? And where does it come from?

The roles of the elements that Michael Denton describes in his “Privileged Species” series of books and videos, particularly in The miracle of the cell (2020) and the miracle of man (2022), are truly fascinating: especially metalloenzymes like iron, copper, and magnesium, not to mention the demanding requirements of common elements like oxygen, nitrogen, and (of course) carbon. However, it was never his intention to discuss every element on the periodic table. His work may galvanize others to help raise the case for the “pre-fitness” of the universe for complex life. We recently discussed another element you overlooked, phosphorus, which adds to the argument. Boron has a similar story to tell.

Nothing boring about boron

Boron, element 5 on the periodic table, is called a “metalloid” because, being between metals and nonmetals, it shares some properties with both. With 5 protons and 3 to 9 neutrons (boron-10 and boron-11 being the most common isotopes in nature), boron has three valence electrons in its outer shell that can form many compounds. It is never found in its elemental form naturally, but more than 100 boron-containing compounds with hydrogen, oxygen, carbon, nitrogen, sodium, chlorine, and even aluminum are known. Many boron compounds, such as boric acid, are soluble in water. In its amorphous elemental form, boron is a brown powder that burns with green flames (see video demonstration below). In fact, the green color in many fireworks comes from boron. Boron compounds have long been used to ignite rocket fuels from the days of Apollo to today’s SpaceX missions.

Before going into its functions in biology, readers may be interested to know that boron compounds have many uses in everyday life: in hand soap (Boraxo), roof tiles, charcoal, glass, ceramics, nuclear shielding, makeup, semiconductors, magnets and much more. more, as the US Borax Company likes to boast. Many have heard of the historic teams of 20 mules that hauled borax through Death Valley and delivered it to the Mojave, 165 miles away, a ten-day ordeal for intrepid miners and their mules in the 1880s. Further to the southwest, there is a small town called Boron in the Mojave desert that is the site of the largest borax mine in the world. It supplies half of the world’s borates and boric acid. The other half is supplied by Turkey, where even larger deposits may exist untapped.

For such a simple atom, boron is surprisingly rare in the universe. Atomic physicists believe that it is produced in small amounts by spallation reactions with cosmic rays or in supernova explosions, but not by stellar nucleosynthesis. This raises questions about how Earth got its supply, a topic we’ll return to shortly. Naturally occurring boron minerals called borates can be found throughout the earth’s crust, at the bottom of the ocean, and in volcanic deposits. If it runs out on the ground, the leaves turn yellow, but too much is toxic to plants. Farmers know that supplementing boron in fertilizers can increase crop yields to some extent. In general, biology does not seem hungry for boron.

So why isn’t boron incorporated into biomolecules? It is located right next to carbon in the period table, but it is extremely different in its actions. Like bromine, boron participates in the synthesis of important compounds without residing in them. As an essential trace element, boron acts as a regulator and facilitator of important biochemical pathways; for example, it can prolong the half-life of vitamin D and thus increase its bioavailability. It plays essential roles in the production of hormones. Plants depend on boron for the construction of their cell walls, and animals depend on it for bone formation. US Borax explains its many functions in plant life:

The boron is an essential micronutrientintegral part of the life cycle of a plant. Required only in small quantitiesboron is needed by plants to control flowering, pollen production, germination and the development of seeds and fruits.Boron also ensures the healthy transport of water, nutrients and organic compounds to growing portions of the plant….

As plants extract borates from the soil, boron is distributed throughout stems, leaves, roots, and other structures. When people eat foods derived from plants, such as fruits, vegetables, nuts, and legumes, they normally absorb small amounts of boron. [Emphasis added.]

Most people get enough boron from plant sources like apples, coffee, legumes, and potatoes. We only need about 1.2 to 3 mg of boron per day, but “there’s nothing boring about boron,” Lara Pizzorno wrote in the jJournal of Integrative Medicine (2015). Consider his staggering list of benefits we get from the small amounts of this element we eat:

Boron has been shown to be an important trace mineral because (1) it is essential for the growth and maintenance of bone; (2) improve a lot wound healing; (3) beneficially impacts the body’s use of estrogen, testosterone and vitamin D; (4) increases magnesium absorption; (5) reduces levels of inflammatory biomarkers, such as hs-CRP and TNF-α; (6) raises antioxidant levels enzymes, such as SOD, catalase, and glutathione peroxidase; (7) protects against pesticide-induced oxidative stress Y heavy metal toxicity; (8) improves brain electrical activity, cognitive performance, and short-term memory in the elderly; (9) influences the formation and activity of key biomolecules, such as SAM-e and NAD+; (10) has shown preventive and therapeutic effects in a number of cancerssuch as prostate, cervical, and lung cancers and multiple and non-Hodgkin’s lymphoma; and (11) can help improve side effects from traditional chemotherapy agents

Geological Availability of Boron

Now that we are convinced of the benefits of boron, some may want to monitor their boron intake or even ask their doctors about supplementation if they are at risk. But where did Earth’s boron come from? As stated above, it is relatively rare in nature, so there shouldn’t be large numbers in the solar nebula from which the rocky planets are thought to have formed. This has led some to speculate that the boron was delivered to earth in a “late layer” of chondrites. That seems strange, though, because one might wonder where those objects got it if not from the solar nebula. Earth got its boron though, now it’s here. It could be assumed that plate tectonics would recycle it, as it does in other elemental cycles (eg carbon, nitrogen).

However, even taking Earth’s current boron budget as given, another issue was raised in a May 6, 2022 article by Liang Yuan and Gerd Steinle-Neumann at Geophysical Investigation Letters. According to their models and calculations, most of the boron should have sunk into the Earth’s core because, at high temperatures and pressures, it sticks to iron.

Plate tectonics promotes the transport of surface rocks into the mantle, producing much of its chemical heterogeneity. Boron, a quintessential crustal element, is often used as an indicator of crustal contributions when found in mantle rocks and is therefore one of the central tools in geochemistry to track recycling/mixing in the mantle. Using quantum mechanical calculations, we find that the chemical behavior of boron changes from lithophilic (rock-loving) to siderophilic (iron-loving) under conditions of pressure and temperature relevant for nucleus formation. Therefore, a lot of boron may have been transported into the core, and the core may be the largest boron reservoir on Earth, rather than the crust.

In other words, the molten iron, as it sank to the core, should have carried most of this scarce element with it. In fact, the two researchers believe that half of Earth’s boron budget is now stored in the core. How can it get up to the crust where plants and animals depend on it?

This opens a question that might interest design advocates looking for more evidence of Denton’s “pre-fitness” argument. Do the circumference and mass of our planet determine the availability of boron? Was there a timing problem that prevented a runaway depletion of boron to the core? As the authors state, “As metallic iron is present predominantly in the core and probably at a percentage level throughout the mantle, its impact on the Earth’s boron budget deserves consideration.” Equal consideration must be given to the requirements for any habitable planet capable of supporting complex life. I have not seen boron availability discussed by Denton or in the privileged planet by Gonzalez and Richards (2004).

The authors mention that certain diamonds (Type IIb) contain excess boron. Other geochemists have taken that as an indicator of tectonic recycling, but these authors challenge that interpretation. “Instead of the boron in type IIb diamonds representing crustal recycling, its predicted siderophilic nature suggests the fingerprint of a metallic deposit.” However, the repository cannot be in the kernel:

The hypothesis of a central contribution to the Type IIb boron signature is highly conjectural like what requires more than 2,000 km of vertical migration of dense core components with minimal boron dilution firms

They suggest that molten iron moved into the mantle, taking boron with it, and that diamonds gushed out from there. (Diamonds can suddenly come to the surface from the mantle in rapid volcanic explosions called kimberlite eruptions.) Although they suggest some isotopic evidence of mantle deposits, their solution also seems highly conjectural. Unless evidence for a self-sustaining boron cycle can be established, one could assume that complex life appeared on Earth at a special time due to the limiting factor of boron availability.

The fact is that the Earth’s surface now appears to have abundant boron for living organisms, even if industrial demand requires extracting as much as can be found in isolated places like the deserts of California and certain provinces of Turkey. In that sense, the boron budget resembles the phosphorous budget in support of Denton’s “pre-fitness” argument. This topic seems primed for some good design-based research!

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