Example: imagine putting one dirty shirt in the laundry basket and then another dirty shirt and then another dirty shirt. The shirt you put in first is going to be the oldest shirt, then the next shirt u put in is the old shirt, and the last shirt is the newest one. That’s the same thing when it comes to layers! One rock of layer was put in one year and then another was out the year after. The one at the bottom is the oldest one because it was the first one put there.