Origin of Life

Radio astronomers have found that organic molecules (including amino acids), which might have played an important role in the formation of life, are present in dust clouds in outer space. Organic molecules are also known to be present in meteors that have fallen to Earth's surface. These observations provide further evidence that chemicals important for the genesis of life may have been present on the early Earth. The presence of complex organic compounds outside of our solar system suggests that the formation of compounds important for life is more likely than once thought.

The presence of organic compounds in outer space also suggests to a few scientists that life may not have actually originated on Earth. Instead, they suggest that abiogenesis may have occurred somewhere in outer space, and that organisms later arrived on Earth. Most researchers discount this "panspermia" hypothesis, because they feel that ionizing radiation and the great extremes of temperature in space would have killed any organisms before they could have reached the Earth. However, the discovery of living bacteria that can suggest intense extremes of radiation and heat has made this objection less compelling in recent years. The suggestion of an extraterrestrial origin of life suffers from the greater drawback that it merely shifts the mystery of abiogenesis from Earth to another place in the universe.

Other researchers suggest that organic precursors to life arrived on Earth aboard meteors or comets. Once here, these organic compounds arranged themselves into molecules that eventually led to the development of life. This theory simplifies the problem of explaining the origin of life by suggesting that the formation of simple organic compounds did not have to take place on Earth.

The genesis of organisms is not yet satisfactorily explained by any extant theory of the origin of life. However, given that life is the most complex chemical process in the Universe and that the chemical basis of reproduction (DNA and RNA) has been known to scientists for less than 50 years (with many details still unraveled), it would be extremely hasty to conclude that science cannot explain the origin of life. The Miller-type experiments and astronomical observations show that chemicals essential to life occur spontaneously under many conditions, and have established an essential point in the case for abiogenesis. The fact that the earliest-known life-forms (eukaryotic cells) were far simpler than later life-forms is also highly suggestive of an even earlier, simpler stage—a bridge between non-reproducing chemistry and life chemistry. Scientists still seek to understand the likely nature of that bridge.