Urey and his experimental contraption |
Many have pondered on the question of the origins of life. We have spent a millenium dissecting life's heirachy, from biosphere to, ecosystems to populations, to communities, to kingdoms and phyla mapped out by Linneaus, to organisms, to cells first discovered by Anton Von Leeuwenhoek, to organelles, to molecules. In the 50's Crick and Watson discovered the DNA, the blue print of life that regulates protein synthesis, which explains how life could be sustained and evolve with this spell-bounding concoction of deoxyribose, a nitrogenic base and a phosphate compound. Still, Crick and Watson does not answer where life came from, but simply how life functions. 4 Billion years ago, the Earth was a hotpot churning, magma, water, and methane; but how did life appear out of the not-so-thin air that veiled early Earth? Russian scientist I. Oparin proposed that life emerged from abiotic synthesis, meaning that life is a concoction of abiotic compounds that somehow became animate.
To prove Oparin's point, Scientists Stanley Miller and Harold Urey (a proponent of Oparin's theory) from the University of Chicago set out to find the answer.
They came up with an idea of an experiment, although obvious in hindsight, it was a novelty at the time. Since Urey and his team had discovered a series of compounds present in early Earth from his previous studies, he and Miller wanted to recreate the conditions of early Earth to see whether a concoction of these lifeless compounds turn into something "living". Here's what they did:
Research Rationale/ Investigation Question
Miller, a PhD student of Urey, wanted to know whether early Earth conditions could conjure and permit the existence of life. So through interactions of natural phenomena and the prevalent compounds abundant in early Earth, Miller proposed that somehow, organic matter would emerge. To put it simply, how did life came about in this inhospitable infant planet?
An artistic depiction of the inhospitable early Earth with all the magma, comets and gasses |
Experimental Design
How exactly will Miller do this? Well, it was established that the Earth 4 billion years ago was hot to say the least, as volcanoes spat out lava into the oceans, and tipping the ocean towards its boiling point. Water evaporates as a result and then condensed, forming thunderheads. Miller simulated this orderly chaos in a system of glass veins, connected to electrodes, cold-water jackets and burners.
As given in his original lab report, Miller mixed a solution of water, methane, ammonia and hydrogen, all are compounds believed to exist in our your planet. The solution was placed in a sealed flask, then heated over a burner, mimicking the volcanic heat. The solution begins to evaporate, and the steam shot up from the flask through a tube to another glass chamber, but this one has nothing but a Tesla coil. The gas was shocked repetitively, simulating early Earth's incessant thunderstorms. Then the steam travels down the tube through a cold-water jacket for it to condense, then trapped in a U- shaped bend (trap) in the glass tube. This process was repeated for a week in this hermetic glass environment.
The trapped substance are then extracted and investigated.
Variables
Independent Variable: The gases and compounds Miller used in the experiment to model that of early Earth.
Dependent Variable: Types of substances found in Miller's processed "soup" trapped in the U-shaped bend on the glass apparatus.
Control Variable:
1) Sterilized glass contraptions, free from all organisms
2) Burner Temperature
3) Electrode/Tesla coil voltage and configuration
4) Cooling Jacket Temperature
5) Hermetic qualities of the glass contraption
(apparatus sealed immediately after its contents are in place)
Results & Analysis
The result? 5 variants of Amino Acids swimming in the processed "soup". Amino acids are the building blocks of Proteins which are produced and synthesized by our DNA's to regulate cell and bodily functions. These amino acids are not random ones, but those found predominantly in organisms. Other acids were extracted too, but only in trace amounts.
Here are the compounds in Miller's "soup" Source: University of Indiana |
Conclusion
The results were mind blowing, it proves that abiogenesis, purported by Oparin, Urey's late colleague, is rather true. Life came from an inorganic origin as the conception of Amino Acids indicated in the Miller-Urey Experiment. It provided ground for future studies of how early earth compounds could create life. This experiment decoded the mystery of life to its molecular level... really?
Limitations and Challenges of the Miller-Urey Experiment
The aura of awe was short lived for the Miller-Urey experiment as it was soon bombarded by claims that the proposed substance mixed in his early Earth solution could never have existed then.(Lane) Why? Since it is clear that asteroids have been pelting Earth since it's conception, the asteroids would have destroyed the earth's atmosphere, rendering water and other compounds non-existent. Those claims soon fell out of favor as asteroids discovered in Australia seemed to actually provided Earth with these compounds for they are made out of "dirty ice" that contained components of Amino Acids. Again, the experiment was under fire when contemporary scientists contended that the volcanic eruptions could produce carbon dioxide in the atmosphere and Miller had not include it in his solution. So these scientists added CO2 into their own Miller-Urey experimental contraptions and found out that there are even more variety of Amino Acids present in their "soup"! Further research were conducted on Miller's original flask containing the soup; which yields another surprising result: there are more (15) Amino Acids in the flask than what Miller had originally calculated.
All in all, although the experiment seemed to be bulletproof it never explained how the Amino Acids form it's primary, secondary and curled into its tertiary functional structure in proteins or where the DNA came from, at least it found us a place to start. Life was not conjured by a divine being, nor was it a creation of extraterrestrials, but from a series of chemical serendipities that turned inanimate molecules into us. It proved how simple it is for the building blocks of life, amino acids for proteins, fatty acids for lipids, nucleotides for DNA and RNA, and monosacchrides for carbohydrates. All of this could be synthesized by simply tweaking the recipe of Miller's primodorial soup; a little bit more carbon dioxide here, a bit more methane there, and there's ATP, glucose, and a dozen types of amino acids! The hard part is to figure out how these organic building blocks come together into a living entity. This is a subject for another day, but at least, the Miller-Urey experiment made it possible to even contemplate on these matter.
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