Final answer:
Uniformitarianism suggests that the slow geological processes we observe today have been shaping Earth throughout its history, implying the Earth's age is great, which is supported by radioactive dating methods indicating an age of around 4.5 billion years.
Step-by-step explanation:
The principle of uniformitarianism, first put forth by James Hutton and later expanded by Charles Lyell, posits that the same geological processes we observe shaping the Earth's surface today have similarly been at work throughout Earth's history. These processes, like erosion, sedimentation, and volcanic activity, typically operate over very long timescales.
This understanding leads us to conclude that the age of Earth is great because the slow and gradual nature of these processes requires immense periods to produce the significant geological features we see. For instance, the formation of vast mountain ranges, the meandering paths of rivers carving out valleys, and the stratification seen within the rock record with embedded fossils all indicate a long and complex history.
Support for the immense age of Earth is provided by radioactive dating methods, such as uranium-238 dating, which estimate the age of the oldest rocks and meteorites to be around 4.5 billion years. This timeframe allows for the slow geological processes suggested by uniformitarianism to take place. Furthermore, the consistency observed in these processes offers a reliable means of interpreting the geological past and predicting future changes, reinforcing the concept of a very old Earth.