The statement "Earth's surface is constantly changing" is a key reason why it can be challenging to determine the age of the Earth. Geological processes such as erosion, sedimentation, tectonic activity, and volcanic eruptions continuously alter the Earth's surface, making it difficult to assess the age of specific rock layers or formations.
While scientists have developed methods to estimate the age of the Earth, such as radiometric dating, the complexities of geological processes do introduce uncertainties. However, it should be noted that the age of Earth has been estimated to be about 4.5 billion years through various scientific techniques.