Debating the age of planet Earth

A while back there was this man named James Ussher, a scholar, who used religion and knowledge of the subject to trace back the dates of past events to estimate the age of the Earth, which he claimed to be 6,000 years old. From what I saw, the scientists probably started to suspect different because as you can see the rocks have many, many layers. My guess is that it takes a while to for at least one layer of rock. Another reason is because the rocks are shaped and scultped quite a bit, not by man, but like from years and years of erosion. The rocks are built up HUGE, so it must have taken a while.