The Ancient Greeks аre knоwn fоr the use оf visuаl imаges/art as a political propaganda.
25.2 Origins оf LifeThe оrigin оf life on Eаrth remаins а mystery, and scientists use various lines of scientific exploration to try to piece together the puzzle of how it began. The early atmosphere of Earth, around 4.6 billion years ago during the Hadean eon, was likely composed primarily of methane, ammonia, and water vapor, with no free oxygen. One scenario for the origin of life is that it originated in the chemically rich oceans of early Earth, composed of a dilute, hot, smelly soup of ammonia, formaldehyde, formic acid, cyanide, methane, hydrogen sulfide, and organic hydrocarbons. Organic molecules, the basis of all living organisms, may have originated through various means, such as chemical reactions in the early Earth's oceans, lightning, meteorite impacts, or even extraterrestrial origins. The Tagish Lake meteorite, for example, is a rocky, carbon-based meteorite that landed in British Columbia in 2000 and was found to contain nearly 3% organic matter, including amino acids and carboxylic and sulfonic acids, which suggests that some organic molecules may have had extraterrestrial origins.One of the key experiments in prebiotic chemistry is the Miller-Urey experiment, conducted by American chemists Stanley L. Miller and Harold C. Urey in 1953. They attempted to reproduce the conditions in the Earth's primitive oceans under a reducing atmosphere, which they believed was composed primarily of carbon dioxide, nitrogen gas, and water vapor, along with hydrogen gas and compounds with hydrogen atoms bonded to other light elements, such as sulfur, nitrogen, and carbon. They assembled a reducing atmosphere rich in hydrogen with no oxygen over liquid water, maintained it at a temperature somewhat below 100°C, and provided it with a natural energy source: simulated lightning in the form of sparks. They found that a variety of organic molecules, including amino acids, were formed due to these conditions, suggesting that the process of forming these molecules may have occurred on early Earth. However, the experiment has been criticized for not accurately replicating the early Earth conditions, and the jury is still out on the veracity of their hypothesis.On the information storage and expression side, a popular model posits that an RNA world predated the modern DNA-based world. This arises from the observation that RNA can both catalyze chemical reactions and store genetic information. In this scenario RNA, rather than DNA, was the first nucleic acid that permitted self-replication, an important step toward life. Later, DNA, which is more stable than RNA, took over the information storage function. Proteins, with their greater molecular diversity, gained the enzymatic function.