[artplumber]

Originally posted by legion
I was pondering today. Assuming evolution is correct, how did life begin? Initially, life would have had to appear "spontaneously". If life did appear spontaneously, one would assume this process would be repeatable, so why the need for reproduction? If the process is repeatable, why haven't we been able to witness or recreate it?

The (generally stated) theory is that there was a big soup of chemicals being radiated by both sun and cosmic and others (do we need to get into this?). This gave the chemicals enough energy to bond/attempt to bond multiple times in multiple ways. Enough of these new compounds are attempted that self-replicators appear - probably RNA first and amino acids appear. RNA begets DNA and complex proteins, as RNA's begin to encode amino acid sequencing. The proteins become associated with other chemicals, and capable of inducing chemical change (enzymatic activity). Along the way cell walls appear, and some of the proteins associate......

The key is a lot of time and interactions, because there are finite (though very small) chances that the radiation + chemicals = something useful or self replicating. The earth is no longer the "primordial soup" hence is no longer capable of producing these kinds of interactions. Several steps in this cascade have been demonstrated in labs, but not a complete generation of cell from soup + energy...