In 1863, Charles Darwin commented that it was a futile exercise to try to apply scientific thought to this origin of origins, when the first living things took shape on a hitherto lifeless planet. We are so used to the idea of an Earth crammed with life in every niche that it is hard to picture the barren world of four billion years ago, when the seas were newly formed and the planet itself was a mere half a billion years old. Most scientists prefer to assume that the molecules that constituted the earliest organisms arose from simpler, small molecules formed by non-biological processes on the young Earth. Proteins are long chains of smaller molecules called amino acids, linked together. Much of the work on the origin of life has focused on the question of how amino acids came into being and how they got linked into proteins.
Amino acids contain primarily carbon, hydrogen, oxygen and nitrogen atoms.
Although the molecules of amino acids are small and simple in comparison with proteins, they are elaborate when compared with the molecules of these gases. But the step from mixtures of crude gases to sophisticated amino acids is not as troublesome as it might seem. In 1953, chemists Harold Urey and Stanley Miller at the University of Chicago showed that they could make a few amino acids simply by mixing ammonia, hydrogen, methane and water vapour in a glass jar and zapping it with electrical discharges. This, they suggested, would be a little like lightning blasting through the primeval skies. Urey and Miller's experiment was pivotal in persuading scientists that understanding the chemical origin of life is not a hopeless quest.