Life came about whenever the conditions were...
[Q] Suitable...
...suitable. Our planet, the earth, is assumed to be 4.7 billion years old, so it took several hundred million years for it to cool down, to develop a chemistry in which these reactions could come about, so life couldn't be much older than 4 billion years. And we say, 'Well, when the conditions were all right, life was here'. And then it took another 3 billion year before a single cell started to differentiate and before multicellular organisms came about. So life as such came very quickly, while the evolution then took its time. So this is one of the big requirements, we started asking the question: what is necessary in order for life to come? We said reproduction. Without reproduction, no evolution, no selection, no evolution. Reproduction requires a particular kind of molecule, namely the nucleic acid. It requires that one building block binds preferably to another one which we call complementary. In the nucleic acid it's the A with the U or the A with the T, and the G with the C. So whenever you have a sequence of these letters you produce by copying a complementary one, like in photography you produce a negative of your... and the negative can then be converted into the positive...