Examples of uniformitarianism include magma cooling and crystallizing, ocean basins filling up, rivers flooding and landmasses experiencing erosion. These processes are things that people can observe in laboratory analogues or in nature.
Uniformitarianism is a concept created by Charles Lyell to describe his version of geology. This concept states that all processes that change the earth remain the same throughout time. Scientists today know that some earth-changing processes are not at play today, such as massive solar debris assaulting the earth. The opposite is also true because plate tectonics, as scientists know them today, did not exist in early Earth history.