As understood by modern geologists, the principle of uniformitarianism implies that .
a. the Earth has always had the same basic appearance that it has today.
b. igneous, metamorphic, and sedimentary rocks are uniformly mixed throughout the crust.
c. physical processes observed today (such as erosion and volcanic eruptions) have been active in the past at approximately the same rates.
d. physical processes observed today (such as erosion and volcanic eruption) occurred much more rapidly in the past, quickly sculpting the Earth’s surface.