Jeffrey Bada, Scripps Institution of Oceanography University of California, San Diego
Jeff - In the early part of the 20th century several people had proposed that organic compounds were made directly on the Earth and this formed a prebiotic soup. Eventually out of this maturing prebiotic soup somehow life evolved. Up to the time of Urey’s thinking on this no one had succeeded in making or demonstrating how you could make organic compounds in a simulated Earth environment. Urey’s idea that you had a different atmosphere was a new one. He presented a lecture at the University of Chicago in 1952 and one of the people in the audience was a young graduate student, Stanley Miller, who was intrigued by this experiment. Afterwards he went to Urey and suggested that he do this experiment for his PhD thesis.
Chris - What did he do?
Jeff - Well, the first thing that Urey said was no, it was too risky an experiment for a graduate student to carry out. Stanley persevered and the first thing they had to consider is what kind of apparatus or how you test this idea. They decided to come up with the apparatus we see in front of you which is designed to mimic the ocean-atmosphere interaction on the early Earth. You have one flask in which you have water and this water is boiled. It goes up and circulates into this other flask which is full of gas which is considered to be a model of the atmosphere.
Chris - That would have contained some hydrogen, some ammonia and some methane to simulate the environment of the early Earth?
Jeff - That’s correct. You’d have methane and ammonia in this flask here which represents the atmosphere. Then you have these two electrodes. These electrodes are where you can apply this spark which would simulate lightning.
Chris - How would he have actually made the sparks then?
Jeff - To make a spark he would use this thing here called a Tesla coil which is something very similar to what you see in Frankenstein movies which generates an electric discharge. I’ll plug this in right now and you can hear this. So now you take this Tesla coil and you apply it directly to the electrodes. That generates a spark inside the flask where the gases are. This is the way energy is injected into this system.
Chris - When he sparked a mixture like that what did he find?
Jeff - He let the spark run and he boiled the water to last for about a week. One of the things he noticed right away is this whole thing turned brown. It got really goopy. One of the remarkable things was that it contained a number of amino acids. Amino acids are the compounds that make up proteins in all living organisms. They’re considered to be essential molecules for life. In this simple experiment he’d taken methane, ammonium and hydrogen. In the presence of water a spark made these proteins. It was a remarkable experiment. What’s amazing about this is that he actually saved aliquots or portions of this water solution from his original experiment. We didn’t realise this ‘til earlier this year when we found some old boxes of his in my laboratory. Inside were these little phials that were clearly marked to show that they came from these early 1953 experiments.
Chris - Did you say, let’s see what the power of modern chemistry can tell us about what’s in these flasks?
Jeff - I was extremely interested in what these might tell us today using the modern analytical tools we have at our disposal. I had two motivations and Stanley died last year. I wanted to go back and revisit and see what the diversity of compounds actually was that he may have missed. More importantly, we realised we also had samples from a couple of other variants of the apparatus that he’d not really adequately investigated at all. He’d done some preliminary analysis but had not done a very rigorous analysis of the products from those apparatus. I was really intrigued by those: especially one of them which we thought might represent an early volcanic system on the earth.
Chris - When you went back and analysed the samples he’d stored what did you find?
Jeff - What’s interesting is that the ones from what we call the classic apparatus like you see in front of us here: we pretty much showed that the major amino acids were just like he’d found before. Then there were a whole number of lesser amino acids. We could expand the inventory of compounds that he had actually made. We more or less tripled the number that he’d found.
Chris - Putting all that together, what does this tell us about the early Earth? Apart from the fact that Stanley Miller could well have been right. What does this tell us about where the building blocks of life probably came from and the environment on the early Earth that gave rise to them?
Jeff - Today many geochemists think that the atmosphere as a whole did not contain methane and hydrogen like Stanley used in his original experiment. As a result you were left with the puzzle again: where did the raw materials necessary for the origin of life come from? The variant of this that he had only partly tested (and we re-investigated it) show that if you have a localised environment such as an island volcanic system on the early Earth and you were releasing volcanic gases in that they’d be immediately subjected to volcanic lightning and these compounds would have been synthesised in a localised environment rather than a global environment. You can imagine early Earth being covered by hundred of these little volcanic islands, acting as little prebiotic factories. All of them would be contributing to the prebiotic soup. I think this demonstrates that the idea of making compounds directly on the early Earth via processes that Miller imagines in 1953 is still very much relevant today.