"After watching the slideshow, speculate about why early geologists may have begun to suspect that the Earth was older than 6,000 years."

I think early geologists thought the Earth was older than 6,000 years because they saw rock formations and trenches that look like water was there to break away at the rocks. If the areas were small then maybe 6,000 years would be right but I don't think the water would completely disappear after only 6,000 years. 6,000 may sound like a big number but compared to the universe and space things it's a really short time. That's why scientists would think Earth's older than 6,000 years old.