How Did Earth Get Its Phosphorus?

The element phosphorus is hard to get to a planet’s surface where it is needed.

Phosphorus, abbreviated P with atomic number 15, is an essential element in all living organisms. How do organisms use phosphorus?

• Phosphorus is an essential element in nucleic acids (DNA, RNA).
• The energy molecule ATP has three phosphate groups. A cell spends enormous effort recycling ATP.
• Phosphorylation is an important regulatory step in many cell processes.
• Cell membranes are composed of phospholipids.
• Bones and tooth enamel get their hardness from hydroxyapatite, a phosphorus-containing mineral.
• Phosphorus is taken up by plants from the soil. Its availability can be a limiting factor in ecosystems.
• Lack of phosphorus can cause malnutrition.

“Oxidative phosphorylation” builds ATP in cells. A chain of complex molecular machines in mitochondria and chloroplasts sets up a proton gradient by carefully extracting electrons from the digestion of our food and passing them through a sequence of reactions (the citric acid cycle), with oxygen as the final acceptor in the electron transport chain. The resulting proton gradient then powers ATP synthase, a rotary engine, that uses the energy to “snap” phosphate groups onto ADP in three reaction centers (see animation by CMI). The ATP molecules can then be sent throughout the cell to power numerous enzymatic reactions that require the energy, such as the walking kinesins that carry cargo, and the numerous enzymes that operate on DNA in the nucleus.

For all its value to life, phosphorus can also be toxic. Some of the most potent neurotoxins and pesticides contain phosphorus.

Molecular machines at work in a living cell (Illustra Media)

A highly reactive atom, phosphorus is never found in its elemental form on earth. Its elemental abundance is one gram per kilogram in Earth’s crust, about 16 times as plentiful as copper. On our planet, most of it is found in insoluble rocks. Phosphate mines have much of the element from the decomposed remains of living organisms.

It would be hard to imagine a habitable planet without phosphorus, because most astrobiologists recognize the uniqueness of nucleic acids, ATP and phospholipids for cells. So this poses a question: how did Earth become blessed with so much of this element?

Planetary Sources of Phosphorus

An article on NASA’s Astrobiology Magazine purports to tell us “How Phosphorus Came In from the Cold.” Below the pretentious headline of this just-so story, we begin to see problems: “phosphorus is rare” in interplanetary dust clouds. “It is even more scarce in the rest of the Solar System,” Sarah Wild writes.

“Phosphorus is one of the key elements in biology,” says Matthew Pasek, an astrobiologist and geochemist at the University of South Florida.

Unlike the other elements essential for life, phosphorus is mainly found in solid form, whereas the likes of hydrogen, oxygen and nitrogen are often found as a gas. “[Studying phosphorus] keeps us grounded in actual hard rock samples. Unlike the others, there is no obvious gas form, so has to come from rock sources,” Pasek says. “We hope to tie that eventually to biology and life.”

Some meteorites contain phosphorus. The problem, then, is how to get those rocks to Earth in sufficient quantities to season the crust with it. Secular cosmologists believe that all the elements beyond lithium (atomic number 3) were “cooked” by supernovae. Phosphorus, therefore, had to come from a supernova, then get incorporated into interstellar dust clouds, from which they believe planetary systems were made. Pasek worries, though, in his recent paper in Icarus, that “Phosphorus would not have been present as a volatile throughout much of the Solar nebula.”

Through a convoluted series of steps, Pasek brings phosphorus in from the cold outer reaches of the solar system by suggesting that it existed in a rare gaseous form called phosphine (PH₃) in the cold outer reaches of the Solar System beyond Saturn. (Out to Saturn, it would have been locked up in solids.) From there, Pasek has the problem of getting that phosphide gas to Earth. Also, meteorites from those far reaches could have brought phosphorus to Earth in the form of phosphides. How they could have been distributed equally on the early earth was not addressed.

One critic of Pasek’s model says that it is “contentious that gas movement toward the Sun, which was not modeled in the paper, could be faster than the diffusion of gas away from the Sun.” It would seem that the latter would predominate.

This is an ongoing problem for astrobiologists, in other words. But it’s fun to get paid for thinking about problems that may not have a naturalistic solution. “The work was supported through NASA’s Emerging Worlds Program,” the article ends. “NASA Astrobiology provides resources for this and other Research and Analysis programs within the NASA Science Mission Directorate (SMD) that solicit proposals relevant to astrobiology research.” NASA money, of course, is taxpayer money.

Maybe we need to add another zone to our list of habitable zones: the “Phosphorus Availability Zone.” But this is only a problem for materialists. The Creator tells us in His word that He “made the world to be inhabited” (Isaiah 45:18). Obviously he put the ingredients required for life where they were needed, in the abundances required.

See more about habitability requirements in Dr Henry Richter’s book, Spacecraft Earth: A Guide for Passengers, chapter one.

For earlier articles on phosphorus and biology, see:

• Most exoplanets are not habitable (26 June 2018)
• Why astrobiologists hammer planets (26 Sept 2016)
• Fooling around with OOL (31 May 2010).
• Invent animals: Just add phosphorus (11 June 2007)

or search on “phosphorus” in the search bar.