What is uniformitarianism?
Uniformitarianism is the assumption that the natural processes which have occurred in the geological past apply to this day, as well as the future.
Uniformitarianism is the concept that natural geological processes which occur today have occurred at approximately the same rate and intensity as they have in the distant past and will continue to do so in the future.
As an example, think of a volcano which erupts, spewing out lava which forms basalt. Knowing that geological processes remain relatively the same throughout Earth's history, you can conclude that every time you see basalt, that it formed from cooling lava.
1. Flowing lava:
2. Lava cooling to form basalt:
Simply put, uniformitarianism may be put into the phrase, "The present is the key to the past." This phrase tells us that if we learn about how geological processes occur today, we can determine how these geological processes formed the landforms and rocks that we can observe today.