Scientists from the University of Colorado have made a surprising find, that if true, will help rewrite the history of life on ancient (pre-biotic) Earth. Published in the April 7 issue of Science Express by doctoral student Feng Tian and associates at the university's Laboratory for Atmospheric and Space Physics with Hans De Sterck of the University of Waterloo, the paper suggests that the amount of hydrogen in early Earth was higher than currently thought. The study concludes that the traditional models estimating hydrogen escape from Earth's atmosphere several billions of years ago are flawed, and about 40 percent of the early atmosphere was hydrogen, implying a more favorable climate for the production of pre-biotic organic compounds like amino acids, and ultimately, life.

Early Earth Mural (Courtesy: AMNH)If true, this has a lot of implications. In a hydrogen-poor atmosphere, it is harder for amino acids (constituents of proteins) to be created. This has led scientists to believe that life first started near the under-sea hydrothermal vents, where the concentration of hydrogen (from water and hydrogen sulfide) is relatively high. But with a hydrogen-rich atmosphere, with or without a lot of carbon dioxide, the production of organic compounds with the help of electrical discharge or photochemical reactions may have been efficient. Once formed on land, the amino acids might have accumulated in the oceans or in bays, lakes and swamps, enhancing potential birthplaces for life.
The study suggests that the carbon dioxide-rich, hydrogen-poor Mars and Venus-like model of Earth's early atmosphere that scientists have been working with for the last 25 years is incorrect, and the escape of hydrogen from Earth's early atmosphere was probably two orders of magnitude slower than scientists previously believed. According to Tian, the escape of hydrogen was low due to the lower temperatures in the upper atmosphere, and the losses were more than compensated by hydrogen release by the volcanoes.
All this makes the old experiments by Stanley Miller and Harold Urey (where they simulated ancient Earth in a glass enclosure as a methane and ammonia rich atmosphere, ultraviolet light and lightning discharges, and managed to generate four amino acids) relevant again. However, in this new scenario, it is a hydrogen and CO₂-dominated atmosphere that leads to the production of organic molecules, not the methane and ammonia atmosphere used in Miller's experiment.
More needs to be studied. Now, we suddenly have two competing theories: 1) Amino acids were first created on land by a hydrogen-rich atmosphere, and 2) Amino acids were created near hydrothermal vents. Only more research will tell which of these (or perhaps both) is the way life first started on Earth.