Science, Part 77
Question 1: Explain the concept of “life’s last common ancestor,” and describe some of the characteristics such an organism must have possessed.
Answer 1: Louis Pasteur disproved the hypothesis of the spontaneous generation of life through his work with bacteria; he proved that even microorganisms are bred from “parents” with similar attributes. The work of Charles Darwin demonstrated that complex organisms evolve from simpler ones by the process of natural selection. Taken together, these scientific discoveries suggest that all of the life currently on Earth could have evolved from a single, simple, original organism—“life’s last common ancestor.” This organism must have possessed the capabilities to store information regarding function and reproduction in nucleic acids and to replicate that information with random variations which would have led to the development of different traits. This ancestor must have been constituted of carbon-rich elements and must have contained proteins formed of one set of 20 amino acids, including enzymes to spawn vital processes.
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Question 2: Explain the Miller-Urey experiment.
Answer 2: The Miller-Urey experiment, performed at the University of Chicago in 1953 by Harold Urey and Stanley Miller, proved that prebiotic chemistry could have produced amino acids, the basic molecules of life. Chemicals thought to have been present in the atmosphere of early Earth (methane, hydrogen, water, and ammonia) were introduced into a glass bulb to replicate the atmosphere. Another bulb was filled with water to simulate the ocean; this bulb was heated to replicate the effect of the sun. The two bulbs were connected with tubing, which allowed evaporated material in the “atmosphere” to return to the “ocean.” Electrodes in the tubing exposed this primordial soup to “lightning.” After a few weeks had passed, the two men analyzed the liquid in the contraption, and discovered that the chemical reactions which had taken place produced several amino acids, indicating the feasibility of the creation of molecules basic to life by prebiotic chemistry. These molecules could have accumulated and led to the chemical evolution of increasingly complex life forms.
Question 3: Discuss some alternate theories for the formation of the basic molecules of life.
Answer 3: Some scientists have theorized that the basic molecules of life may have arrived on Earth from an extraterrestrial source. A carbonaceous meteorite, which hit Australia several years after the Miller-Urey experiment, was found to contain the same amino acids produced by the experiment in roughly the same proportions. The purine bases of nucleic acids (adenine and guanine) have been shown to exist in meteorites as well. Also, complex molecules vital to life on Earth have been detected in a nebula. Clay theory suggests that organic molecules arose progressively from the “replication platform” of silicate crystals in solution.
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