`yearDiscovered` should give an approximate year if possible

[andrejewski]

Some elements have their year of discovery marked as "Ancient" which I'd like to narrow down to at least some approximate integer date (even if it is a negative to represent BC). This adds more context to the data but also better normalizes it so users don't have to check for number or string when working with the values.

[sabidhasan]

My suggestion would be to use -infinity as the value

This way, you have a datatype of number and still keep the "unknown" factor. Some elements we really can't put a date on, even roughly.