Lecture 4: The Origin of Life 1 PDF

**Lecture 4 The Origin of Life 1** **Transcribed by [TurboScribe.ai](https://turboscribe.ai/?ref=docx_export_upsell). [Go Unlimited](https://turboscribe.ai/subscribed?ref=docx_export_upsell) to remove this message.** In this and the next seven lectures, I\'m going to be dealing with each topic in...

**Lecture 4 The Origin of Life 1** **Transcribed by [TurboScribe.ai](https://turboscribe.ai/?ref=docx_export_upsell). [Go Unlimited](https://turboscribe.ai/subscribed?ref=docx_export_upsell) to remove this message.** In this and the next seven lectures, I\'m going to be dealing with each topic in two parts. The first part will focus on the evidence for an evolutionary view, and the second part for each topic will focus on the evidence against the evolutionary view. I\'ll start with the origin of life. Darwin actually didn\'t treat the origin of life in the origin of species, other than to add to the second and later editions that he thought life might have been breathed by a creator into one form or a few. He later wrote to his friend Joseph Hooker that he regretted truckling to public opinion with this, that is, submitting to public opinion by saying something he didn\'t mean. What he really meant, he explained to Joseph Hooker, was that he thought life began in a warm little pond with some ammonia and phosphoric salts and heat and light and electricity as energy sources. Darwin thought these would form into a simple protein, which would then go on to make more complex molecules. In the 1920s, Russian scientist Alexander Oparin and British scientist J.B.S. Haldane proposed that the atmosphere on the early Earth consisted of what are called reducing molecules, especially methane, ammonia, and hydrogen, along with some water vapor. In their proposal, lightning could have formed the building blocks of proteins, that is amino acids, in the atmosphere, and these could have then dissolved in the ocean to make a dilute primordial soup. Their proposal went untested for many years until 1953, when chemist Stanley Miller, in the lab of his Ph.D. supervisor Harold Urey, put together a glass apparatus, a closed glass apparatus with tubes, in which he circulated methane, ammonia, hydrogen, and water vapor, and the water vapor came from a bowl of water at the bottom that he boiled. So, as he boiled the water, the methane, ammonia, and hydrogen circulated past him. After a week, Miller analyzed a brown tarry substance that had accumulated at the bottom of the apparatus, and in it he found several amino acids, that is the building blocks of proteins. He published the experiment, and it immediately became a sensation, because it convinced some people that scientists had now solved the problem of at least the early steps in the origin of life. The apparatus and the description of the experiment found its way into most biology textbooks, which were out to convince students of the materialistic origin of life. In the 1980s, though, geochemists concluded that the early Earth\'s atmosphere wasn\'t like that at all. Instead, they thought, it consisted of the gases emitted by modern volcanoes, mainly carbon dioxide, nitrogen, and water vapor, though some carbon monoxide, which is a reducing gas, was, is emitted as well. Because the Earth\'s gravity is so light, the hydrogen in the atmosphere, if there was any, would have escaped to space, in their opinion. In 1983, Stanley Miller repeated his experiment with a more realistic mixture, this time carbon dioxide and carbon monoxide, and he was able to produce, with this experiment, a small amount of glycine, which is the simplest amino acid. In 2014, the textbook Biology by Kenneth Miller and Joseph Levine reported that this 1983 experiment and others, with different mixtures, produced similar results. So, according to the textbook, the Miller-Urey experiment was pretty much intact. In 2008, one of Miller\'s graduate students, Jeffrey Botta, and his colleagues re-examined a 1955 experiment that had been done by Miller. They found, in their re-analysis, more amino acids than Miller had originally reported. And the thing that made this experiment different from the 1953 experiment was that Miller had used a small nozzle to inject steam into the stream of gases. Instead of just passing them over boiling water, he injected the steam into them. Other researchers have since shown that steam from volcanoes attracts lightning. So, in 2008, Botta and his colleagues called a 1955 Miller experiment the Miller Volcanic Spark Discharge Experiment. In 2014, Campbell\'s Biology reported that amino acids formed under conditions that simulated a volcanic eruption. Not everyone was convinced, though. It seems that proteins need DNA. In a normal cell, they\'re synthesized based on DNA sequences. But DNA is very hard to produce without other DNA. So, it\'s almost impossible to conceive of DNA as being the first biological molecule. But since proteins seem to need DNA, it\'s kind of hard to conceive of them too, even though you can get some amino acids from a Miller-Urey experiment. So, some biologists proposed that RNA, which is the chemical intermediate between DNA and protein, that RNA preceded the other two molecules in the 1980s. Two molecular biologists showed that RNA can act like an enzyme, that is, like a protein that speeds up reactions between other molecules. Walter Gilbert, another biologist, then reported, or hypothesized, that RNA might actually be able to replicate itself without protein. Normally, it would need protein to replicate. But if it could act as its own enzyme, it might replicate itself. And out of this, the idea of the RNA world grew. It\'s still an open question of whether RNA could form abiotically, without life, on the early Earth. But many origin of life researchers are optimistic. Recently, Jack Szostak, who won a Nobel Prize for chromosome discoveries, wrote, simple chemistry in diverse environments on the early Earth led to emergence of ever more complex chemistry, and ultimately to the synthesis of the critical biological building blocks. At some point, the assembly of these materials into primitive cells enabled the emergence of Darwinian evolutionary behavior, followed by the gradual evolution of more complex life forms leading to modern life. So, this is the scenario envisioned by origin of life researchers. But is it true? Could it have happened this way? In my next lecture, I\'ll take a look at it to see how realistic it is. **Transcribed by [TurboScribe.ai](https://turboscribe.ai/?ref=docx_export_upsell). [Go Unlimited](https://turboscribe.ai/subscribed?ref=docx_export_upsell) to remove this message.**