Newer layers of earth form on top of older layers, so as we dig, we can see further back in time. Comparing the fossils between the layers can offer evidence of change.
Phyletic gradualism - slow, but constant gradual change; supported by transitional species in the fossil record
Punctuated equilibrium- long periods of no change followed by short periods of rapid change. Can also be supported by the fossil record when no transitional species are found.