In the past, I gave consideration to the "gap theory", and I haven't altogether abandoned all aspects of it. However, regardless of whether for countless ages the planet earth itself existed prior to the 7 day creation 6000 odd years ago, (there being no hint that the planet itself was created at that time, only redesigned somewhat), death, which came as a result of sin, didn't exist prior to the fall of Adam and Eve in the garden. Nothing died prior to sin, which biblically puts to rest any concept of theistic or natural evolution. The gap remains maybe, who really knows, but there could be no life that lived and died during that period.