Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Miller Experiment
Name: Jordan T.
Status: Other
Age: 20s
Location: N/A
Country: N/A
Date: June 2002


Question:
I am reading a book in which there is a discussion about a chemical experiment and I need a bit of clarification. In this experiment, Stanley Miller at the University of Chicago took a mixture of ammonia, methane, and hydrogen, shot electricity through it and found that amino acids had been formed. This proved that life could have evolved out of nonlife on primitive Earth.

The counterpoint offered to this is that ammonia, methane, and hydrogen were not abundant on primitive Earth but, rather, water, carbon dioxide and nitrogen dominated the atmosphere and the experiment wouldn't work with that mixture. The man who brings that up seems very confident that it invalidates the experiment.

My confusion arises because it seems to me that H2O, CO2, and N2 could be split by electricity and the resulting atoms could realign themselves to yield NH4, methane (a carbon compound), and H2. So, in my mind, the experiment is not invalid, it just skips a step.

I would very much appreciate clarification of why this is not possible.



Replies:
Several points:

1. For starters, no one knows what the composition of the atmosphere was in early geological times. Harold Urey and Stanley Miller (Urey's graduate student) did the "sparking" experiments that you refer to. Many other groups, for example biologist Carl Sagan (of "billions and billions of stars fame"), subsequently performed similar experiments using different types and amounts of starting gases, different energy sources, different total pressures, and on and on.

NONE OF THESE EXPERIMENTS "PROVES" THAT LIFE ON EARTH STARTED BY ANY ONE OF THESE MECHANISMS. Their results are conjectures (Conjectures in science are fine, scientists do it all the time. But do not confuse conjecture with "proof" or with "cause -----> effect" ). Conjectures are educated guesses. What these primordial atmosphere conjectures demonstrate is: It is NOT IMPOSSIBLE that life MIGHT have started by one or more of these mechanisms. That is a far weaker claim than: Life DID start by one of these mechanisms.

2. No one even knows whether there were bodies of liquid water on earth during those eons. If there was not, where and how did liquid water come to cover the majority of the surface of the earth?

3. And then there is the problem of oxygen (O2) gas. Oxygen gas is very inhospitable to small organic molecules. It tends to oxidize (read that burn) them back into CO2, N2, and H2O. But if there were no free oxygen (O2) gas, when and how did it become 20% of our atmosphere and how did these primordial life-forms survive in its presence?

4. And what about the problem of chirality? Any molecule that has a point or plane of symmetry with respect to reflection has two configurations that are un-superimposable (mirror images like a pair of gloves -- one for the left hand, and one for the right hand). If you try to put the right hand glove on the left hand it does not fit. The thumb and little finger are in the wrong places. Both of these configurations are formed in these high energy atmospheric model experiments. The two configurations are distinguished by whether the molecule rotates a beam of linearly polarized light to the right (clock-wise) or to the left (anti-clock-wise). However, virtually all molecules involved in life processes (sugars, proteins, enzymes, etc.) are LEFT HANDED. The body cannot even digest the right handed forms, and in principle if you were fed a diet composed solely of the right handed forms, you could starve to death! Why did Nature choose the left handed form to create life? If both forms are produced in equal amounts (which is the case in many chemical reactions that are not sensitive to the "handed-ness" of the molecule), why aren't there two complementary life forms on earth -- one left handed and one right handed? Is this in some complicated way related to the fact that Nature chose to make the Universe out of matter, rather than anti-matter. The best current cosmology theories predict that matter and anti-matter were formed in equal amounts, but the Universe is almost all matter and anti-matter must be "created" by nuclear processes and other artificial high energy interactions.

I am not sure I clarified your concern about the primordial atmosphere, but I hope I did clarify that there are more unanswered questions than answered questions.

Vince Calder



Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory