Suppose no stars more massive than about 2 msun had ever formed. would life as we know it have been able to develop? why or why not?

Stars with masses less than two times the mass of the Sun can produce elements only up to carbon and oxygen. More massive elements are not produced, and some of these more massive elements ( calcium, phosphorus, iron) are essential for the forms of life found on Earth.

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue

d. air pressure decreases as altitude increases.