Question

Describe the conditions thought to be present on early earth (before life) and relate these conditions to the origin of organic molecules

Before life evolved on Earth, the mantle and crust released carbon dioxide, nitrogen, and other heavier gases through volcanic activity. The gravitational field of the Earth held these gases close to the planet resulting in a new atmosphere. This early atmosphere consisted mainly of methane, carbon dioxide, ammonia, hydrogen, nitrogen and water vapor. Since all of the atmospheric oxygen reacted with other elements present on early Earth, there was no free oxygen in the early atmosphere for approximately 2 billion years (i.e., Earth’s atmosphere was “reducing”). A famous experiment done by Stanley Miller suggested that an electrical charge, such as lightning, in a reducing atmosphere (as thought to have been present on early Earth) could produce simple organic compounds. Please refer to a previous question from our archives to find out more concerning this experiment and the theories surrounding the origins of life: http://nai.arc.nasa.gov/astrobio/astrobio_detail.cfm?ID=188 As stated in the archived question above, a newer theory suggests that organic molecules could have been delivered to early Earth via asteroid or cometary impacts, thus seeding the Earth with the appropriate precursors necessary for the evolution of more complex systems. Check out these web sites for more information: http://science.nasa.gov/headlines/y2001/ast05apr_1.htm http://www.resa.net/nasa/origins_life.htm Madalyn Edwards, NASA Astrobiology Institue
August 19, 2002