The Shadow Biosphere

A few years ago I wrote an article for Cryptid Culture magazine #7 about the microbial cryptids that may be lurking all around us. Since the magazine has been defunct for a while now, I thought I'd post that article in full here. 

You can still purchase copies of Cryptid Culture from Blurb. Definitely check it out. There were some great articles.

THE SHADOW BIOSPHERE

In our search for unknown creatures we often focus on large, impressive cryptids- Mothman, Sasquatch, the Jersey Devil, Nessie. Beasts that, if they do exist, would be extremely rare and inhabit the periphery of humanity’s territory.

But what if there are uncountable hordes of unidentified organisms all around us? What if they are in the soil beneath our feet? In the damp spots in our basements? Even lurking inside our very bodies? What if there are whole unknown domains of life whose existence we have never even suspected because they are too small to be seen with the naked eye and so radically different from conventional Earthly life that we do not even have the proper tools to detect them? What if there is an entire Shadow Biosphere (a term originally coined by researchers Carol Cleland and Shelley Copley of the University of Colorado in 2005) lurking all around us? 

The exact origin of life on Earth is not currently known, though scientists have posed many possibilities. Some have speculated that life coalesced out of the mineral-rich waters around hot springs or deep-sea hydrothermal vents. Others have wondered if the basic building blocks of life arose in warm tidal pools or on the surface of carbon-based matter floating in droplets of sea spray. Still others have wondered if the components of life might have been brought to Earth on icy comets. It’s possible- even likely- that simple life arose multiple times and in multiple forms in these and many other crucibles on the early Earth. 

At some point, though, one type of life predominated and took over every ecological niche on the planet. This kind of life is highly plastic in the form it takes: bacteria, amoebae, algae, jellyfish, dinosaurs, humans. Organisms very different in form and structure, yet all sharing the same fundamental building blocks. Their genetic information is wrapped up in double-helices of DNA constructed from four bases: guanine, cytosine, adenine and thymine . Their bodies are built and controlled by proteins and enzymes made of 20 different amino acids. And many of their support structures- hair, wood, cell membranes, etc- are constructed from carbohydrates.

But what if other life forms made from different sets of building blocks also developed in those dawn crucibles? What if they used a molecular structure besides DNA to hold genetic information? What if they utilized more than the familiar 20 amino acids to build their proteins? Or a different set of amino acids entirely? Even if such organisms did evolve they must surely have gone extinct early on, out-competed by life that dominates the Earth today? Otherwise we surely would have found evidence of them.

Perhaps not, though. The majority of living things on Earth are prokaryotes- unicellular microbes too small for us to see with the naked eye.  Under a microscope, most prokaryotes look fairly similar. Their cells are either shaped like pills, spheres or twisting corkscrews. You can’t tell what species a prokaryote is just by looking at it.

But this external simplicity and uniformity hides a universe of metabolic diversity. Some prokaryotes can photosynthesize like plants. Some can obtain energy from salt or sulfur. Some live off metals or oil. Some even feed on radioactive materials like uranium.  And of course, there are the more commonly known microbes that parasitize other living organisms. To identify prokaryote species, scientists have developed tools and techniques to detect the various enzymes, chemicals, and other molecular components that allow them to live and feed in these unique ways. Additionally, since prokaryotes are so small and numerous, these techniques are not performed on individual specimens. Instead, they are tested in a “shotgun” fashion on a sample of, say, soil or pond water to detect the overall presence and abundance of certain metabolic components.   These techniques assume, however, that the organisms being examined are composed of the DNA, proteins, and other building blocks of regular terrestrial life.  They would not find denizens of the Shadow Biosphere if their structures and genetic material are different from what we currently know.

There is actually a precedence for discovering a completely new domain of life. Up until the late 1970s all life on Earth was placed into two broad categories based on the structure of their cells. Eukaryote cells have lots of smaller metabolism-performing structures called organelles inside them, including a nucleus to contain DNA, mitochondria to generate energy, and, in the case of plants and algae, chloroplasts to photosynthesize. All animals, plants, algae, fungi, and many single-celled organisms such as diatoms, paramecia, and amoebae are eukaryotes.

The aforementioned prokaryotes, by contrast, have no organelles. Their DNA and all metabolic enzymes float freely in the cell.  For decades all prokaryotes were assumed to be bacteria. In the late 1970s, however, researchers noticed that some prokaryotes had proteins and other chemical structures that were vastly different from those found in the majority of these microbes. What’s more, these strange prokaryotes were genetically closer to each other than they were to any other bacteria. It soon became clear that these organisms were a whole new domain of life that researchers dubbed the Archaea. 

It’s important to note that even though archaea differ from eukaryotes and bacteria in some structural ways, they still utilize DNA and the 20 amino acids found in the other two groups.  Archaea may have evolved separately from the other domains, but they are still ultimately descended from the same distant ancestor as the others. They are not part of a Shadow Biosphere. The point of this story is to illustrate the fact that that unique microbial organisms can indeed be lurking all around us without being detected.

  So, is there any evidence for a Shadow Biosphere? One possible clue to their presence is a phenomenon known as desert varnish. In arid regions around the world, exposed rock outcroppings frequently develop a thin red or black coating of iron, manganese, silica and clay particles. Native peoples around the world have created petroglyph images on these rocks by scrapping away this thin dark patina to expose the lighter rock underneath. Though desert varnish has been extensively studied, its exact origins are not known. Many scientists think it is caused by chemical weathering or by the slow action of bacteria or archaea living on the surface of the rocks. Some, though, have suggested that the dark patinas could have been deposited by the unknown organisms of the Shadow Biosphere. Testing this hypothesis would require developing techniques, which I will discuss a little later, to detect traces of non-traditional life forms.

It’s possible that some of these Earthly aliens have actually been found. In 1996 geologist Phillipa Uwins and her team discovered microscopic filament-like structures on pieces of freshly fractured sandstone they had pulled from 2-3 miles below the ocean floor. Soon, the filaments, which Uwins  dubbed “nanobes”, were found to be growing on equipment and containers in her lab that had come into contact with the samples. Experimentation found that the nanobes would also grow and even multiply on freshly fractured rock samples. Testing with DAPI staining- a technique for finding double stranded nucleic acids like DNA- produced a strong positive result, indicating that these filaments had genetic material and were thus alive.  That revelation created quite a conundrum, though, because these nanobes were one-tenth smaller than even the smallest known bacteria or archaea. At that size, a conventional organism would simply be too small to contain the genetic material and proteins necessary for life. Could nanobes have different chemical structures for carrying out life’s functions? Uwins and her colleagues are still hesitant to definitively claim nanobes are a new form of life, or even alive at all. More research is required to determine the exact nature of these structures.  Nevertheless, they are another tantalizing clue to the existence of an unsuspected Shadow Biosphere lurking all around us. 

All this speculation begs the question: how would one find evidence of the Shadow Biosphere if its denizens cannot be detected by techniques that target known Earth life? One possibility would be to develop experiments that look for other amino acids in the environment beyond the familiar 20. Another possible method would be to develop a chemical reagent that can distinguish between typical DNA and other genetic material that might have different bases besides guanine, cytosine, adenine, and thymine. This reagent could be used to stain a sample of cells gathered from, say, a soil sample. Any cells that were not stained could potentially possess a gene-encoding structure different from typical DNA.

As I stated at the beginning, while the big, bizarre cryptids like Mothman and Thunderbirds may be the most popular, some of the strangest, truly unique organisms on Earth may be lurking under our very feet beyond the limits of what our eyes and scientific instruments can see. The trick to finding them may require looking beyond what we currently understand as life on this planet.   

SELECTED REFERENCES

Cleland, C. E. (2007). Epistemological issues in the study of microbial life: Alternative terran biospheres? Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences, 38(4), 847-861.

Cleland, C. E., & Copley, S. D. (2005). The possibility of alternative microbial life on Earth. International Journal of Astrobiology, 4(3 & 4), 165-173.

Uwins, P. J. R., Webb, R. I, & Taylor, A. P. (1998). Novel nano-organisms from Australian sandstones. American Mineralogist, 83(11-12, Part 2): 1541-1550.