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There was an experiment the replicated atmosphere of young earth. Electricity was used to simulate lighting. I have heard that the problem with this experiment is that the atmosphere they created in the experiment is not the same as what scientists believe young earth's atmosphere was really like. Is this true?
Answer 1:

There are a number of experiments currently happening to study the origins of life on Earth. Some of these look to thermal vents at the bottom of the ocean while others look to the chemistry of the atmosphere and sources of energy such as lightning. The important early experiment in this study was performed by Stanley Miller and Harold Urey in 1953. They looked at the atmospheres of major planets such as Jupiter and hypothesized that Earth's early atmosphere (before the hydrogen drifted into space) would resemble these other planets. I think this is the atmosphere you refer to. More recent research suggests that the Earth's early atmosphere was more rich in nitrogen, carbon dioxide, and water vapor than Miller and Urey assumed. This more oxidizing atmosphere would be less accommodating for early amino acid development but some people still think it would have been suitable for early life.

The exact answer remains unresolved. Visit the interesting site here about new theory of earth's early evolution

The following link talks about how life adapted to Earth's changing early atmosphere.
http://www.space.com/scienceastronomy/planetearth/earth_archaean_010716.html

Answer 2:

Well at the time of the UREY MILLER famous experiment, the prevailing opinion was that the Earth's atmosphere was a reducing one. That is, there was not only no free oxygen (O2) but that diatomic hydrogen was present. Hence the primary species in the reducing atmosphere would have been H2,CH4,NH3 and H2S. However, since that time the pendulum has swung a bit and most geologists believe that the most likely state of the Earth early atmosphere was a non oxidizing one (so called Abelson model). In this model again there is NO FREE OXYGEN to speak of. However the primary constituents are CO2, H2O, SO2/SO3 and N2. It is more difficult to synthesize by electrical discharges etc.amino acids in an Abelson atmosphere than a Urey-Miller (reducing) atmosphere.There are not many robust constraints we have on the composition of the early atmosphere although there are ways to get at the problem. Free oxygen (O2) first accumulated about 2 billion years ago...due to photosynthetic bacteria


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