Ever heard of an angular unconformity? This is a type of geologic feature, first discovered at the end of the 18th century, that is completely incompatible with "flood geology" and a young Earth. This kind of feature consists of rock layers which are tilted at an angle, are sheared off on top, and which have another set of rock layers laid horizontally on top of them. This implies the following: the rock layers were laid over some length of time, at the bottom of an ocean. Then geologic forces lifted the layers up and folded them (into hills or mountains). These then eroded (over some length of time). Then, later, what was left of these mountains (tilted rock layers) was immersed under water again (in a lake or sea), where new rock layers were laid down. Finally, sometime later, these rock layers were lifted upwards again, where further erosion revealed them for us to see them. Note the sequence of events, each taking a certain amount of time. A lot of time. One can imagine the Grand Canyon being cut in days by some enormous flood, and one can imagine rock layers being laid down in various locations as a result of the flood. But one cannot imagine how an angular unconformity was created in this way.
There are numerous other geological evidences for an old Earth. One more example: Coral reefs have annual growth rings, just like trees. Coral reefs commonly have hundreds of thousands of these.