Explain the Miller-Urey experiment. How could it have been changed to make it more realistic?

The experiment demonstrated how some biological molecules, such as simple amino acids, could have arisen abiotically, under conditions similar to early Earth. Water, methane, ammonia and hydrogen were the chemicals used to produce the results of the experiment, therefore to produce similar results, one would have to have these chemicals present to initiate the reactions, this could lead to life arising on another planet