German alchemist Hennig Brand discovered the element phosphorus in 1669. One peculiar observation about this element is the glow that elemental phosphorus gives in ambient conditions. It is the glow that signals chemical reactivity, or the formation of oxygen-phosphorus compounds. Thus, phosphorus tends to bond to oxygen quickly when in the elemental state.
We find phosphorus in DNA, cell walls, and in the energetics of life. So, how does life incorporate phosphorus if it is unavailable? The question of phosphorus incorporation in the molecules of life has perplexed many generations of biologists and chemists.
Fossilized Evidence of First Life
Early Earth history leaves little evidence of ‘first life’ for the intrepid scientist. Weathering and geologic processes have worn the fossilized evidence from the face of the Earth. However, time and wind cannot wipe away enduring chemical markers; the late heavy bombardment posed an intriguing solution to the question of “where was the missing phosphorus?”
A break appeared in publication form in the mid-2000s with the recognition of iron-nickel meteorites as a source for the correct phosphorus. A research group from the University of Arizona posed the following solution: Iron-nickel meteors incorporate phosphorus within their crystal lattice in a form that is conducive to life’s chemistry. Subsequent publications clarified the initial findings, but like any detective story, this theory needs to be fleshed out.
Earth-bound Phosphorus and Biochemistry
Setting a timeline from a 2006 journal article in Philosophical Transactions of the Royal Society, Professor Allan Schwartz of the UK details how scientists could not explain how Earth-bound phosphorus was incorporated into biochemistry. The crux of the problem lay in an energy barrier for Earth-bound phosphorus. The majority of known phosphorus was ‘tied-up’ with any form of oxygen or water. In this fashion, the solvent of life prevented a crucial step of life from taking place.
However, in 2005, a publication appeared in the journal Astrobiology detailing the ground-breaking finding of Pasek and Lauretta; their work centered upon phosphorus-containing meteorites. As their paper explains in keen detail, meteorites from Antarctica came in two distinct categories: Meteorites containing ‘useful’ phosphorus and meteorites containing ‘spent’ phosphorus. When the researchers examined the ‘useful’ phosphorus meteorites more closely, the researchers came to the conclusion that upon appropriate experimental conditions, the embedded phosphorus could be liberated for use in Earth’s biochemistry.
The ‘spent’ phosphorus meteorites, on the other hand, could not be utilized in life’s chemistry; in fact, the embedded phosphorus bore an uncanny resemblance to Earth’s current and past, wet chemistry. (Although the choices seem simplistic, it took a leap of scientific intuition to subject iron-nickel meteorites to early Earth conditions— a stroke of genius, in my opinion.)
Early Phosphorus Breakthroughs
After Pasek attained a tenure track position at the University of South Florida in 2006, the work with phosphorus-containing meteorites continues to prosper. The latest pinnacle in the story came during mid-2013, when the Proceedings of the National Academy of Sciences published the following article from the research group: Evidence for reactive reduced phosphorus species in the early Archean ocean.
The study delves into the amount of ‘useful’ phosphorus found in sedimentary layers in Australia; it is solid evidence for ‘useful’ phosphorus entering Earth’s early timeline during the Late Heavy Bombardment era in pre-history.
Phosphorus and Early Life
Many scientists believe that life took a foothold immediately following the Late Heavy Bombardment. Although researchers still hotly debate the mechanism of life, the origins of the foothold of phosphorus seems to be on its way to a solution.