As a Christian scientist, Dr. Bohlin is open to examining the theories of both young-earth and old-earth scientists to explain what we can observe today. The Grand Canyon provides an excellent venue to consider the theories of both groups on how the geological layers were formed and when this occured.
If the door is already attached, swing it open and closed to see how much inertia it has. An average hollow-core door usually weighs around 25 to 30 pounds, so if you can lift or swing the door with minimal effort, it is probably hollow-core. Solid-core doors are usually 25 to 30 pounds heavier than their hollow counterparts, so if the door has some heft to it, it's probably solid-core.
The major advantage to solid core doors is they are more sound deadening than a hollow core door. Another advantage is they are stronger. They will take some abuse without much more than just scratches. The disadvantage is the weight. They are heavy and hard to handle all the way from the lumber yard to your house. The weight of the door can cause some drywall cracking if the door gets slammed hard enough. So if you plan to have any door slamming competition with your spouse or one of your kids; you may not want a solid core door. Another disadvantage is with more wood, more warping can happen. Take care to always apply a finish to all 6 edges (top, bottom, edges and both sides) of the door.