The diameter of the Earth is 7,918 miles or 12,742 kilometers. To be completely accurate I must state that the Earth is not exactly round. It’s about 25 miles wider at the equator than from pole to pole.
The highest mountain on earth is Mt. Everest. It is 29,029 feet or 8,848 meters high.
Now imagine the earth being a big blue marble ball about the diameter of the height of an average sized American man, about 1.8 meters or 1800 millimeters. Picture yourself in a museum, in front of a ball as large as that. Touch that ball, feel how cold and hard it is. And above all, feel how smooth it is.
How high would Mt. Everest be on that ball, if its height were exactly to scale? It would be 1.2 millimeters high. Can you picture 1.2 millimeters?
The left red line is about 1.2 millimeters wide. This is actually a little tricky, because the width and resolution of your screen can change this somewhat. But you get the idea. Pull out a metric ruler and you can see the smallest units are millimeters.
Anyway, it’s very small on that big blue man-high marble ball in front of you. If you rubbed your hand over Mt. Everest, since it is not an abrupt mountain, but a gradual increase over the width of the Himalayas, you might not even feel Mt. Everest.
You definitely would not feel the indentation of the Grand Canyon, since its depth is only about a fifth of the height of Mt. Everest. It would depend on the sensitivity of your hand.
The highest mountain in Earth is negligible when viewed from the scale of the entire globe.