Life as we know it could not exist without phosphorus. I’ve written before about this essential element (here, here), but geochemists know that of the 29 atomic elements required for human life, availability of phosphorus worldwide is restricted by chemical and geological constraints. Astrobiologists therefore consider phosphorus a limiting factor for life on earth and habitable planets, because it is not clear whether it would be expected in planetary crusts or in the stellar disks from which they are presumed to form. Even if it were present, how could it move from the interior to the surface where life needs it?

Based on the profusion of life in every habitat we know here on earth, whether in oceanic, polar, desert, rainforest, or montane ecosystems, I had a hunch that earth somehow “solved” this supply chain problem. Indeed, vast coal seams and fossil fuels speak of even richer ecosystems in the past. Fossils show that each species was well supplied with phosphorus for its ATP, membranes, and DNA. New research indicates surprising ways that our planet distributes phosphorus where it is needed and conserves existing supplies.

Underground Delivery

Three years ago, I noted that a phytoplankton bloom resulted from the Hunga-Tonga volcano (here), suggesting one geological process aiding the supply of phosphorus to the oceans. “The role of volcanoes and orogenic processes in keeping phosphorus plentiful throughout Earth’s history,” I said, “deserves elaboration by design theorists.” 

Though phosphorus is only a trace component of most lavas (Oregon State), its effect must match supply to demand. Observations show that volcanic ash can promote life. This year, news from the University of Hawaii announced that “Kilauea volcano’s ash prompted [the] largest open ocean phytoplankton bloom.” Study co-author David Karl included phosphorus as one of the essential elements delivered by the volcano:

“The waters in the open ocean of the Pacific are nutrient depleted and the addition of volcanic ash, especially iron in the ash, and to a lesser extent other trace elements and possibly phosphate, can stimulate the growth of marine phytoplankton, especially the so-called nitrogen-fixing microbes that can growth in the absence of additional nitrogen,” said Karl. [Emphasis added.]

They mentioned two delivery mechanisms. One was lava flowing into the ocean, warming the deep waters and making them more buoyant. Another mechanism is wind.

The nutrient-rich deep water rising to the sunlit surface stimulated phytoplankton growth, resulting in an extensive plume of microbes offshore of Hawai’i Island. Volcanic ash can be transported much farther distances by winds, especially during explosive eruptions that inject materials high into the atmosphere. 

The wind “supply chain” had reached 1,200 miles to the west of Hawaii in this instance. If a small volcano like Kilauea (pictured at the top) could produce the largest known phytoplankton bloom in the North Pacific, then surely larger volcanoes throughout earth’s history have had the potential to distribute phosphorus worldwide.

Subaerial Delivery

Wind also delivers phosphorus in fine dust particles high up in the atmosphere. Would anyone imagine that dust from the Sahara could supply phosphorus to the Amazon rainforest? That was the surprising conclusion of a NASA report from 2015. Researchers monitored dust plumes from the Sahara with the Calypso satellite, supplementing the orbital images of the plume (see the video below) with ground studies in the Amazon Basin.

But where did the Sahara get its phosphorus? Dr. Hongbin Yu from Goddard Space Flight Center explains that it has been stored within dead microbes that are “remnant in Saharan sands from part of the desert’s past as a lake bed.” 

This trans-continental journey of dust is important because of what is in the dust, Yu said. Specifically the dust picked up from the Bodélé Depression in Chad, an ancient lake bed where rock minerals composed of dead microorganisms are loaded with phosphorus. Phosphorus is an essential nutrient for plant proteins and growth, which the Amazon rain forest depends on in order to flourish.

The Sahara now shares its bounty with the world, transporting phosphorus from “one of the planet’s most desolate places to one of its most fertile.” Surprisingly, Amazonian phosphorus would otherwise be in short supply, the report says. Only some of it can be recycled by decaying organic matter: “some nutrients, including phosphorus, are washed away by rainfall into streams and rivers, draining from the Amazon basin like a slowly leaking bathtub.” 

Of the 182 million tons of Sahara dust lofted by wind annually, only a fraction reaches Amazonia. But remarkably, Amazonia’s shortfall is replenished almost perfectly through this intercontinental aerial delivery mechanism.

The phosphorus that reaches Amazon soils from Saharan dust, an estimated 22,000 tons per year, is about the same amount as that lost from rain and flooding, Yu said.

Commenting on this finding, geographer Dr. Sarah Buckland-Reynolds noticed the match as evidence of engineering design.

Imagine — seemingly ‘random’ wind patterns are now being discovered to be engineered to act as massive Global Automated Fertigation systems carrying just the right amount of dust from a desert ecosystem to a specific tropical ecosystem separated by 3000 miles. It deposits enough phosphorus to replace about the same amount of this essential fertilizing element lost to the local ecosystem! Could this engineering arise from chance?

NOAA continues to monitor the Sahara dust plume with NASA’s GOES-19 satellite. They detected a “giant plume of dust” headed to the United States, showing that North America is another beneficiary of the supply chain (watch this timelapse video of the plume operating day and night). The phosphorus airlift delivers additional benefits to living things, including phenomena for human aesthetic enjoyment:

The dust is due to a two to 2.5-mile-thick layer of the atmosphere, called the Saharan Air Layer, crossing over the Atlantic Ocean. The warmth, dryness and strong winds associated with this layer have been shown to suppress tropical cyclone formation and intensification. 

When it reaches the U.S., it can cause hazy skies as well as vivid sunrises and sunsets as the sun’s rays scatter the dust in the atmosphere.  It can even suppress thunderstorm development over locations where the dust is especially thick.

The Americas are not the only beneficiaries of supply chains in the wind. A 2022 report from Europe’s Copernicus Atmospheric Monitoring Service says that Asia has its own transport hub:

Given its gigantic extension, the Sahara Desert is the main global source of atmospheric dust, but there are other important hotspots around the so-called dust belt. The Gobi Desert is the main dust source in Asia with transport reaching as far as the Hawaiian Islands.

Spain, Scandinavia, the Alps, China, and the Caribbean are mentioned as other beneficiaries of these dust transport chains. Watch the timelapse video to see these transport systems at work, swirling around the globe. While the dust poses some hazards as well (e.g., viruses and other pathogens, respiratory risks, radioactivity), the concentration of these substances is low, and the altitude of the dust usually poses little threat to life at the surface. Measuring 1/10 the width of a human hair on average, the Sahara dust particles can act as condensation nuclei for precipitation far and wide. The overall effect seems to moderate the extremes of hurricanes and droughts while accentuating the benefits of rain and nutrient abundance. That’s quite a system for something as common and mundane as dust! 

Processing Systems for Bioavailable Phosphorus

To be useful, phosphorus must be in the right chemical state. As noted earlier, inorganic phosphate tends to bind to common metal cations, forming poorly soluble minerals. In Nature Communications, three authors commented on recent indications given by another paper in the same journal of active redox cycling of phosphorus on the early earth. Their Figure 2 shows sources of reduced phosphorus from meteor impacts, metamorphism, volcanism, lighting, UV rays, hydrothermal vents, and serpentinization in the crust. These sources could have made soluble phosphorus available to oceanic microbes, they say, but many questions remain.

Another type of interaction of phosphorus with microbes was discussed in Nature Geoscience by Butler et al. The team of five showed that “microbial physiology conserves phosphorus across long-term ecosystem development.” They indicate that underground microbes can double the conservation of phosphorus above ground.

These strategies — which proliferate during primary succession and are maximized in retrogressive, P-depleted ecosystems — uphold microbial carbon limitation, triple modelled P-mineralization potential and can conserve close to double the P contained in the aboveground biomass of vegetation. These findings transform our understanding of terrestrial ecosystems by revealing a strong yet overlooked interplay between the ecophysiology of soil microorganisms and the long-term trajectory of ecosystem development.

In Short, No Shortage

The transport systems and processing systems discussed above help explain why phosphorus, long considered a limiting resource for biological productivity, is actually abundant in nature where and when it is needed. Farmers and gardeners need to mine phosphate and add it to promote growth, yet the biosphere flourishes through its own automated delivery systems. 

Astrobiologists will need to take the presence or absence of these systems into account when estimating the number of habitable planets. On earth, the phosphorus cycle operates so perfectly it might lead an unbiased observer to infer that a designer engineered all these independent processes to work together for a purpose: to showcase a thriving zoo, botanical garden, and marine waterpark partly for the enjoyment and benefit of The Miracle of Man.