Urey-Miller Experiment – A Dead End?


Among the many issues surrounding the origin of life on Earth that must be solved is the origin of small molecules needed to build more complex molecules (like proteins or DNA) necessary to living systems. The first to really attack this problem experimentally with success were Stanley Miller and Harold Urey back in the 1950s.  At that time, Miller was a graduate student of Urey’s at the University of Chicago.  They were operating under the fundamental assumption that the early Earth’s atmosphere was reducing – meaning the atmosphere was full of hydrogen (H2) and lacking in oxygen (O2).  In his ground-breaking experiment, Miller simulated lightning (using a spark-discharge) in such a reducing atmosphere, composed of hydrogen, methane (CH4), and ammonia (NH3), then directed the products towards some water.  To his (and the rest of the scientific community’s) surprise, amongst the products produced were some of the essential amino acids for life (amino acids are the building blocks for proteins, one of the three necessary biomolecules for life along with RNA and DNA).  This was a momentous result!  For many years thereafter, scientists performed further spark-discharge experiments (simulating lightning) searching for – and finding – other necessary building blocks for life.

But, is a reducing atmosphere plausible?  Most now think no.  Rather, the early Earth atmosphere is thought to have been controlled by volcanic outgassing more similar to today’s volcanic emissions – resulting in an atmosphere composed primarily of  carbon dioxide with some nitrogen and water, but with only small amounts of hydrogen.  Unfortunately, this “neutral” atmosphere, similar to the current composition of the atmospheres of Mars and Venus, is essentially a dead-end for spark discharge experiments, with essentially no useful molecules being produced.

So – is the Urey-Miller experiment useless in terms of the production of the first building blocks for life?  Not necessarily according to OB Toon and coworkers at the University of Colorado – they are revamping the reducing atmosphere feasibility by arguing that although the hydrogen levels would have been lower coming from the early Earth volcanoes, the escape rate of hydrogen to space would have been slower, retaining a significant concentration of hydrogen in the atmosphere (see their article published in Science in 2005 for the real science, http://www.sciencemag.org/content/308/5724/1014.abstract).  This would re-validate the Urey-Miller experiments!

So, what is the conclusion??  The short answer is that there still is no consensus within the scientific community as to whether or not spark discharge was a feasible way to make the building blocks needed for life on early Earth.  It is difficult to determine the exact composition of the early atmosphere, and thus scientists are still working on the problem.

What if spark discharge experiments are a dead end?  Is there no hope for the production of these necessary molecules on early Earth?  Should we just give up?  Of course not – there are two other plausible theories on the origin of these molecules: synthesis in hydrothermal vents (spots on the ocean floor where heated water from volcanic activity spews out) and transport from space to Earth by meteors and/or comets (there were many MANY more impacts from these on early Earth).

So, going back to the hype surrounding all origin of life theories, many strictly naturalistic origin of life proponents still maintain the validity of the original Urey-Miller Experiment in public settings (like the Museum of Natural History in Washington D.C., at least as of a few years ago when I last visited…), not communicating the challenges that this original experiment now face within the scientific community.  On the other hand, critics of naturalistic origins completely discount spark-discharge experiments in the origin of life, thereby claiming that there are NO plausible naturalistic routes to the production of simple molecules needed in larger biomolecules (like DNA).  In reality, the scientific community has presented results which lie somewhere in between these two extreme positions.  It is important that both sides of this argument recognize that scientists haven’t quite figured this one out, so taking a strong stance on either side of the fence is probably a little premature…

Historical vs. Operational Science

I have been surfing the internet just browsing some other blogs about the origin of life and have found that a vast majority of them (at least the ones I came across today…) are geared at the Evolution – Intelligent Design/Creation debate.  My biggest problem with these are that the debates end up being solely semantics full of people with agendas who end up writing emotion-driven posts.  The problem that I see with all of these discussions is that we have now gotten to the point where there is no longer any actual science being discussed in these debates.  Instead, the proponents of each side just verbally attack each other, with each side making broad statements that have been bouncing around in the media for years.  What happened to the science??  Ok, now on to some more semantics, but in my view essential to this whole debate.

One of the issues that nearly always comes up is the issue of origins research being “historical science” in comparison to “operational science”.  These words are not usually used in the scientific world, but are often seen in Philosophy of Science discussions or by critics of current origins science in general (i.e. ID proponents).  To the everyday practicing scientist, it doesn’t matter whether your research is geared toward historical or operational science – the methodologies are identical.  Both observe phenomena directly in the lab and draw conclusions from these observations.  The difference lies in the interpretation and dissemination stage – the types of conclusions which are drawn. 

Take the composition of the atmosphere as an example.  Today, atmospheric scientists can directly measure the composition of the atmosphere – from ground based measurements to planes carrying instruments which suck in some air and analyze it.  They can then develop models which can tell us how air packets flow from one region of the Earth to another as well as track chemical changes in the atmosphere in general.  This helps in understanding what happens to ash clouds which are ejected from volcanoes and even how chlorofluorocarbons, or CFCs (which were the major cause of the ozone hole) can impact the environment as a whole.  This is operational science.  A direct observation is made in well-defined conditions and then conclusions are drawn based on those specific conditions.

Making claims about the composition of the atmosphere on prebiotic Earth is much more difficult.  We are unable to directly take measurements of the atmosphere at that point in history, and so instead, we must use secondary sources to help us make educated guesses at what the composition was like (i,e, looking at the composition of rocks in different layers or stages of history).  Although the methods are still the same – we are still making observations (analyzing the rock layers) and then drawing conclusions from those observations, the conclusions that we draw have many more unknowns to them.  No matter what the optimistic scientists claim, we can never truly know what the composition of early Earth was nor how life arose.  Instead, we must just accept that although the historical science we are doing is good science, it will never give us an absolute answer.

It is interesting to me that so many people get so upset about choosing a camp and defending it to the death in regards to origins science.  This is actually quite an ignorant thing to do, and I think that it is the nature of origins science (a nature which is primarily ignored) that prompts such a response.  Origins science is not absolute – it can merely give clues as to plausible routes to life.

The what and why…

This blog is meant for those with a keen interest in the origin of life – not just the politics or the dogmas (although I am sure I will spend my fair share ranting about those issues as well), but a true interest in the cutting edge science being performed today as well as the implicit philosophical repercussions.  Origins science is unique from all other types of scientific research – it relies on the use of current methodologies for the analysis of events which occurred in the past.  Unlike most other modes of science, origin of life research does not allow for any direct observation of the events which the scientists endeavor to explain,and thus, the work is akin to a sleuth following clues in a whodunnit.   Naturally, this prompts much controversy amongst both the scientific community and the public, with backlash from all sides.  This underlies my purpose in starting this blog.  The public, well at least those amongst the public with some interest in scientific findings, are unable to access the pure science themselves, as reputable scientific findings are published in scientific journals, both written for and solely read by scientists.  Thus, I will discuss some of the new (and some old) ideas in origin of life science, and hope that anyone who dares read what I write will take the time to write a comment or two, and maybe learn something along the way.

Actual science coming soon!