Prof. Kasting’s assessment of the claims for the early-Earth atmosphere is far less critical (and over two decades later) than that of a pair of geologists:

“Geological evidence often presented in favor of an early anoxic atmosphere is both contentious and ambiguous. The features that should be present in the geological record had there been such an atmosphere seem to be missing….Ever since the work of Oparin…and the success of the experiments conducted by Miller…the dogma has arisen that Earth’s early atmosphere was anoxic, probably highly reducing…Conjecture and speculation, based on a knowledge of the chemistry of living matter, gave to them the composition of their starting materials, and it would have been surprising if they had not achieved the results they did.”
[Harry Clemmey and Nick Badham. 1982. Oxygen in the Precambrian Atmosphere: An Evaluation of the geological Evidence. GEOLOGY, March, p. 141]

http://www.springerlink.com/content/qx55749700j61652/

With Melvin Calvin’s group:
http://nobelprize.org/nobel_prizes/chemistry/laureates/1961/calvin-bio.html

Some think life may have been brought to Earth, so in that case it would be interesting if the same building blocks that lead to life could have come about independently under the same conditions, but in two different environments. And then when brought together, there was some intermingling of genes.

Really, this is just thinking out loud. I do appreciate the perspective though.

Within this matter of fact statement of the characteristics of laboratory reactions can be found a fundamental problem with the conclusions often drawn from the Miller experiments. It is as impossible to produce amino acids of all one type with random electrical charges as it would be to take a deck of well-shuffled cards and deal a hand of all one color off the top.

Even before tackling the problem of self-replicating DNA, an experiment successfully demonstrating the origins of life would have to identify the environment and conditions necessary to allow random chance to produce the unilateral array of amino acids.

This is not merely a technicality involving the nature of laboratory research, but one of the most important factors in an accurate analysis of the data procured through these experiments.

Regardless, it’s very unlikely that any of the three domains evolved independently. The universal genetic code very strongly suggests a common origin.

Are there respectable theories that life may have independently come about more than once? That is, the Archaebacteria, Eubacteria, and Eukaryotes are each separated from one another in the tree of life, but shouldn’t there be a common ancestor? My understanding is that Archaebacteria are possibly the common ancestor, but also, possibly not.

Then again, if all three groupings have things in common, they don’t necessarily have to be related. The whole analogous/homologous thing where bees and bats developed structures (wings) for flight independent from one another. Whereas the bat’s wings are way more similar to our (humans) arms, which aren’t used for flying–or really locomotion at all.

Yes, yes, many steps away from a non-enzymatic synthesis. But all too often my students (and colleagues) are misled that amino acids cannot be the precursors of nucleic acids.