Question

summarize theories of how life began on Earth

Answer 1

A theory for the "chemical life" could be the theory Stanley Miller tested in the famous Miller–Urey experiment.

Answer 2

What he believe was that the air on earth consisted of water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2). Then lightning hit the molecules creating organic molecules and eventually amino acids that can create proteins. He tested this and put the above gasses into a container and used a pair of electrodes as fake lightnings... using that he was able to create 11 out of 20 amino acids.