In what ways were conditions on early Earth different from those on Modern earth?

Question

$\begin{array}{1 1} (a)\;\text{The early Earth had a layer of ozone} \\ (b)\; \text{The early earth was much cooler} \\ (c)\;\text{ Less ultraviolet radiation penetrated the early atmosphere} \\ (d)\;\text{ The early atmosphere had significant quantities of methane and ammonia. } \end{array}$