I think that the Earth is more than 6,000 years old because in places like the grand canyon you can see all of the layers of rock and you can tell by analyzing the rock how old each level is and what the contests of it are. That makes it so you can accurately date the Earth's age and see the chemical phases it went through. The Grand Canyon was also formed by erosion from the Colorado River, erosion takes a long time to happen, especially in such a dramatic and big way. This also makes me think that the Earth is very old, because that much erosion couldn't happen in 6,000 years.