What is biology?
Biology studies life. Life, defined in an abstract form is the capacity of reproducing. Conceptually any thing with this capacity would be life. Isaac Asimov imagined, for example, life based on silicon (silicon, the chemical element that makes computers has properties very similar to carbon).
In practice, we only know life in our planet, the Earth, and then biology is much more concrete. Biology studies how life beings function.
Life in the Earth at the end can be considered one part of chemistry. In fact, an small fraction of chemistry. Life is based is very few atoms or chemical elements.
We are also an aqueous solution, although we have to analyze it with care because it is not an ideal solution, any of the components are very concentrated.
There are several points making life in the earth very particular:
– Elements used are scarce.
– All living beings are very similar (composition -molecular and cellular structure-, genetic language, chemical reactions).
All these data seem indicate that life appeared only once or perhaps there were several tests and only one survived, or life require conditions that only occurred once. This makes this intriguing.