Recently a young earth friend pronounced me an evolutionist because I believe life has existed on this earth for hundreds of millions of years on this 4.5 billion year old planet. He did not understand that for several decades, leading evolutionists have recognized and acknowledged a number of geologically sudden appearances of new forms of life at widely spaced intervals after long periods of little change. Generally, new forms of life on earth appear rather suddenly after major extinction events.
Leading evolutionists Niles Eldredge and Stephen Jay Gould gave this phenomenon a name several decades ago - punctuated equilibrium. The term is more descriptive than explanatory. Creative theories to account for such rapid, step-like appearance of new species have been proposed, but the theories are not well developed. The theories do not come with convincing supportive evidence.
What do these sudden appearances of new life at widely spaced intervals suggest? They suggest supernatural action by a Creator more clearly than evolutionary processes. They also suggest the "days" of Genesis 1 may indeed be long periods of time. Possible supernatural intervention cannot even be expressed openly by the purveyors of evolution, because it is contrary to the naturalistic explanations held to be necessary by most paleontologists.