Most research into the origin of life is based on one of two theories: Abiogenesis, the assumed generation of life from non-living matter, or Panspermia (sometimes known as Exogenesis) based on the idea that life reached earth from the cosmos.
A number of experiments have been conducted in varying conditions considered to simulate primeval conditions. Best known are those undertaken in the laboratory by Miller and Urey in 1953 which produced amino acids in an electrically charged atmosphere but no life. More recent work using oxidation inhibitors has greatly increased the amino acid yield but has not approached the produced life itself.1
NASA-funded research, undertaken for over 20 years, has included field experiments in pools of heated and sterile water associated with volcanoes in the Kamchatka region of eastern Russia and at the Lassan Volcanic Park in California. Here a “pre-biotic” soup containing the building blocks of proteins and DNA with fatty acids are being poured into a volcanic pool in Kamchatka but they failed to interact, becoming bound with the clay of the site instead.
From this work it has been concluded that geothermal springs and similar extreme environments do not favour membrane formation, seen as a prerequisite to the development of cellular life. An alternative suggestion had been that rock cavities at hydrothermal vents might have provided the structure in which life emerged. 2
The idea that life reached earth from the cosmos is known as panspermia or exogenesis. Mars is considered a prime source as it is similar to Earth with systems of air, water, ice, and geology. Evidence of water, a necessary prerequisite for life, has been found at Melas Chasma on Mars.where water-based processes have created fans of debris as well as the channels through which water and sediment flowed.3 NASA’s Mars Exploration Program seeks to understand whether Mars was or can be, a habitable world.
Meteorites have also been considered a possible source to indicate the existence of life elsewhere in the universe. Examination of meteorites for evidence of fossils or other signs of life however has been inconclusive. In this work the possibility of the contamination of our solar system from the abundance of life on earth, either as a result of meteorite impacts or through transmission by spacecraft, has to be considered. The meteorite which fell near Murchison, Australia in 1969 contains complex organic molecules such as amino acids but scientists are divided as to whether they result from contamination or not.4 The meteorite from Allan Hills, Antarctica (ALH 84001) revealed structures which were considered for a time to be fossil evidence from Mars but this is now largely discounted 5 although the original researchers still consider that the most plausible explanation is that they are life remains.6
The discovery of microscopic red cells in rain in Kerala, Southern India in 2001 led to a suggestion that they might represent extraterrestrial life from space. High resolution electron microscopy revealed internal structures as well as evidence of a replication cycle and have now been identified as Trentepohlia algae spores. 7
Despite laboratory and field simulations it has not been possible to generate life; neither has evidence of life been found elsewhere as a result of NASA’s space programme or the examination of meteorites.