Microevolutionary change might seem too unimportant to account for such amazing evolutionary transitions as the origin of dinosaurs or the radiation of land plants — however, it is not. Microevolution happens on a small time scale — from one generation to the next. When such small changes build up over the course of millions of years, they translate into evolution on a grand scale — in other words, macroevolution!
The four basic evolutionary mechanisms — mutation, migration, genetic drift, and natural selection — can produce major evolutionary change if given enough time. And life on Earth has been accumulating small changes for 3.8 billion years — more than enough time for these simple evolutionary processes to produce its grand history.