Posts Tagged ‘reductants’

Debate has long reined over the mysterious origin of oxygen in our atmosphere. Because oxygen is such a key ingredient in life it would seem necessary for oxygen to be present before life could have formed.  However, the most accepted theory in scientific circles today is that life came first, then came oxygen. But isn’t oxygen needed for life? Here I will briefly introduce the dilemma of oxygen’s origins on earth and the conclusions (or lack there of) it provides.

The story starts with earth. Earth is hungry to consume oxygen. Oxygen reacts with minerals in the earth, with hydrogen in the atmosphere, and dissolved minerals and gases in the ocean. The earth consumes oxygen relentlessly (Catling, 70). The oxygen absorbing substances are called “reductants,” and they are a problem for any source of oxygen (Catling, 69). David Catling, an Astrobiology Professor at the University of Washington writes, “While oxygen appears to be essential for complex life, planets are constructed with chemicals that consume oxygen, so oxygen should not accumulate. Earth’s oxygen rich atmosphere is rather mysterious,” (Catling, 69). In fact, the only way for oxygen to accumulate is for oxygen production to exceed earth’s ability to consume it. So what are the potential sources for oxygen?

There are two sources for oxygen; biological and non-biological. The latter is a process called photodissociation, in which ultraviolet rays break apart water molecules separating the oxygen from the hydrogen. Studies have shown that the rate at which this could occur is the same rate at which hydrogen would escape the atmosphere (Des Marais). However, the rate at which this would occur is hardly sufficient to produce the amount of oxygen present on earth. (Des Marais).

So the only other solution is biological. When organic carbon and pyrite become buried in sediments, mostly from the ocean, oxygen is released (Catling, 69). There is a problem with this theory though because it would require an increase of the burial rate to create the exponential increase needed for oxygen to overwhelm earth’s reductants, yet studies show that carbon burial in sedimentary rock was constant during this period of time in earth’s history (Siegel). So carbon burial cannot be the predominant cause.

oxygen evolution model

The standard uniformitarian model for the evolution of life and chemical compositions in earth’s atmosphere.

However, organic life itself creates oxygen. Cyanobacteria was the first photosynthesizer, and thus the first producer of oxygen (Eden, 33 and Wolfe, 143). Cyanobacteria itself cannot be the cause for the accumulation though because according to current theories and history models cyanobacteria appeared almost a billion years before the oxygen accumulated in earth’s atmosphere. So again, we hit a brick wall. In the end there are a variety of theories explaining the oxygen build up, but there is a reoccurring theme in all of them: Life came before oxygen, because life is the cause of oxygen. As science writer David Biello writes, “Climate, volcanism, plate tectonics all played a key role in regulating the oxygen level during various time periods. Yet no one has come up with a rock-solid test to determine the precise oxygen content of the atmosphere at any given time from the geologic record. But one thing is clear—the origins of oxygen in Earth’s atmosphere derive from one thing: life,” (Biello). This “fact” that oxygen origins come from life is assumed, yet when analyzed, presents a problem that jeopardizes the entire theory of oxygen’s origin.

cyanobacteria

Cyanobacteria. The assumed origin of oxygen on earth.

Oxygen and life have a catch 22 relationship. Oxygen is very harmful to life (Eden, 33). At the same time oxygen is needed to provide the ozone layer which protects life from ultraviolet radiation (UVR)coming from the sun (Perlman & Milder, pp. 121). If Cynobateria came before oxygen, because it is the cause of oxygen, then Cynobacteria would have had to develop several forms of protection to mitigate the damage from UVR: avoidance, scavenging, screening, repair, and programmed cell death (Singh, Hader, and Sinha). However, UVR damage is immediate and the time needed to “evolve” protection against it via natural selection, incredibly slow. So, UVR damage would occur before any such defense mechanisms could evolve.

One seemingly good solution to this problem is water. More specifically, the ocean. If cyanobacteria first evolved in the ocean, the ocean would protect them from UVR, right? Well not exactly. The only way for the ocean to block UVR is if you go deep underwater. At which point the depth is too deep to photosynthesize. The argument then follows, that perhaps life first originated in the ocean, then overtime evolved enough to come up to the surface to photosynthesize without getting burned by UVR.  But even this theory has its own problems. Namely the problem of hydrolosis or “water-splitting.” The US National Academy of Sciences explains, “In water, the assembly of nucleosides from component sugars and nucleobases, the assembly of nucleotides from nucleosides and phosphate, and the assembly of oligonucleotides from nucleotides are all thermodynamically uphill in water. Two amino acids do not spontaneously join in water. Rather, the opposite reaction is thermodynamically favored at any plausible concentrations: polypeptide chains spontaneously hydrolyze in water, yielding their constituent amino acids,” (Luskin). Physicist Richard Morris concurs, “… water tends to break chains of amino acids. If any proteins had formed in the ocean 3.5 billion years ago, they would have quickly disintegrated,” (Morris, 167). Additionally, the cytoplasm of living cells contain essential minerals of potassium, zinc, manganese and phosphate ions. If cells manifested naturally, these minerals would need to be present nearby. But marine environments do not have widespread concentrations of these minerals (Switek). Thus, it is clear, life could not have formed in the ocean.

What we’re left with is a perplexing paradox: Water prevents the formation of life. Oxygen prevents the formation of life. Lack of oxygen prevents the formation of life. Yet the only source of oxygen currently accepted is organic. How can organics be the source of something it requires present in the first place? The only way for life to create oxygen is if the life itself already has built in mechanisms present from the very beginning to protect itself from the outside environment.

Needless to say, the specific details regarding the origin of oxygen remain mysterious. Catling writes, “Although we think we know when oxygen first appeared and rose, we know very little about its rise to the present level, especially about the relationship between atmospheric oxygen and the development of animals,” (Siegel).

As time goes on maybe these issues will be clarified. But the paradox between life and oxygen remains. So much so that it leaves me to postulate the more likely scenario of life being created with infrastructure necessary to survive in its environment. That is, God created an environment for life, and life for an environment. There are just too many problems with a step by step natural origin for all the factors required for the origin of oxygen. As of right now, at least, it is the only answer to this paradox.

Biello, D., (August 2009) “The Origin of Oxygen in Earth’s Atmosphere,”  www.scientificamerican.com

Catling, D., (2008) “Where did the oxygen in the atmosphere come from?” as written in Seventy Mysteries of the Natural World, ed. M.J. Benton, (London: Thames and Hudson)

Des Marais, D.J. (Oct 1999) “Where did the Earth’s atmospheric oxygen come from?” scientificamerican.com

Luskin, C., (Feb 2012) “More Scientists Admit the Mystery of Life’s Origin,” www.evolutionnews.org

Morris, R., (2002) The Big Questions, (Times Books/Henry Holt:New York,NY)

Out of Eden, (2005) (London: Transworld Publishers)

Perlman, D.L. & Milder, J.C. (2004) Practical Ecology for Planners, Developers and Citizens, (Washington, DC: Island Press)

Siegel, L., (July 2003) “The Rise of Oxygen,” Astrobiology Magazine, http://www.astrobio.net

Singh, S.P., Hader, D.P., & Sinha, R.P. (April, 2010) “Cyanobacteria and ultraviolet radiation (UVR) stress: Mitigation Strategies,” as accessed on Feb 18, 2013 at http://www.ncbi.nlm.nih.gov/pubmed/19524071

Switek, B., (February 2012) “Debate Bubbles Over the Origin of Life,” http://www.nature.com

Wolfe, N., (Jan 2013) “Small Small World,” National Geographic