Conducting Miller-Urey Experiments

Summary

The Miller-Urey experiment was a pioneering study regarding the abiotic synthesis of organic compounds with possible relevance to the origins of life. Simple gases were introduced into a glass apparatus and subjected to an electric discharge, simulating the effects of lightning in the primordial Earth’s atmosphere-ocean system. The experiment was conducted for one week, after which, the samples collected from it were analyzed for the chemical building blocks of life.

Abstract

In 1953, Stanley Miller reported the production of biomolecules from simple gaseous starting materials, using an apparatus constructed to simulate the primordial Earth's atmosphere-ocean system. Miller introduced 200 ml of water, 100 mmHg of H₂, 200 mmHg of CH₄, and 200 mmHg of NH₃ into the apparatus, then subjected this mixture, under reflux, to an electric discharge for a week, while the water was simultaneously heated. The purpose of this manuscript is to provide the reader with a general experimental protocol that can be used to conduct a Miller-Urey type spark discharge experiment, using a simplified 3 L reaction flask. Since the experiment involves exposing inflammable gases to a high voltage electric discharge, it is worth highlighting important steps that reduce the risk of explosion. The general procedures described in this work can be extrapolated to design and conduct a wide variety of electric discharge experiments simulating primitive planetary environments.

Introduction

The nature of the origins of life on Earth remains one of the most inscrutable scientific questions. In the 1920s Russian biologist Alexander Oparin and British evolutionary biologist and geneticist John Haldane proposed the concept of a "primordial soup"^1,2, describing the primitive terrestrial oceans containing organic compounds that may have facilitated chemical evolution. However, it wasn't until the 1950s when chemists began to conduct deliberate laboratory studies aimed at understanding how organic molecules could have been synthesized from simple starting materials on the early Earth. One of the first reports to this end was the synthesis of formic a....

Protocol

1. Setting Up a Manifold/Vacuum System

1. Use a glass manifold to introduce gases into the reaction flask. This manifold can be purchased or constructed by a glass-blowing facility, but must include vacuum-tight ports that can be connected to a vacuum system, gas cylinders, a vacuum gauge, and the reaction vessel.
   1. Use ground glass joints and glass plugs with valves on the manifold. Ensure that all O-rings on the plugs are capable of making the necessary seals. If using glass joints, a sufficient amount of vacuum grease can be applied to help make a seal, if necessary. Silicon vacuum grease can be used to avoid potential organic contamination.
   ....

Results

The products synthesized in electric discharge experiments can be quite complex, and there are numerous analytical approaches that can be used to study them. Some of the more commonly used techniques in the literature for analyzing amino acids are discussed here. Chromatographic and mass spectrometric methods are highly informative techniques for analyzing the complex chemical mixtures produced by Miller-Urey type spark discharge experiments. Amino acid analyses can be conducted using o-phthaldialdehyde/N-acetyl.......

Discussion

Numerous steps in the protocol described here are critical for conducting Miller-Urey type experiments safely and correctly. First, all glassware and sample handling tools that will come in contact with the reaction flask or sample need to be sterilized. Sterilization is achieved by thoroughly rinsing the items in question with ultrapure water (18.2 MΩ cm, <5 ppb TOC) and then wrapping them in aluminum foil, prior to pyrolyzing at 500 °C in air for at least 3 hr. Once the equipment has been pyrolyzed and while prepari.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Glass Plugs for Manifold	Chemglass	CG-983-01
High Vacuum Grease	Apiezon	N/A	Type M/N
Silicon High Vacuum Grease	Dow Corning	1597418
Teflon PFA Tubing	McMaster-Carr	51805K54
Ultra-Torr Vacuum Fittings	Swagelok	SS-4-UT-6
Dry Scroll Vacuum Pump	Edwards	A72401905
U-Tube Manometer	Alta-Robbins	100SS
Tungsten Electrodes	Diamond Ground Products	TH2-1/16	2% thoriated
Methanol	Alfa Aesar	N/A	Ultrapure HPLC Grade
Teflon-Coated Magnetic Stir Bar	McMaster-Carr	5678K127
Gaseous NH3	Airgas	AMAHLB	99.99% purity
Gaseous CH4	Airgas	ME UHP300	99.99% purity
Gaseous N2	Airgas	NI UHP300	99.999% purity
Tesla Coil	Electro-Technic Products	15001	Model BD-50E
24 hr Plug-in Basic Timer	General Electric Company	15119
Cleaning Detergent	Alconox	1104
Toluene	Thermo Fisher Scientific	N/A	Optima Grade
Luna Phenyl-Hexyl HPLC Column	Phenomenex	00G-4257-E0	Brand: Luna
Formic Acid	Sigma-Alrich	F0507	Used to make 50 mM ammonium formate