That is when extinction occurs. Hope I helped!
I would think that an unweathered rock would be jagged while a weathered rock would be smooth because of water/wind or what ever weathered it.
As food reaches the end of the esophagus, it enters the stomach through a muscular valve called the lower esophageal sphincter. The stomach secretes acid and enzymes that digest food. Ridges of muscle tissue called rugae line the stomach. The stomach muscles contract periodically, churning food to enhance digestion.Mar 4, 2016