1) The Earth isn't round!
Actually, (like a lot of us) the Earth is a bit plump about the middle. Why? Because it's spinning so fast! The Earth's rotation creates stress on the rocks and the oceans, causing the planet to bulge around the equator. In fact, because the Southern Hemisphere is mostly ocean and because water is easier to move than land, the Earth is a little bit pear-shaped!
2) The tallest mountain is . . . well . . .
You probably said Mount Everest right away. It's true that Everest is the point on Earth farthest from sea level. However, there are at least two challengers to Everest's claim. If you measure base to peak, then Mauna Kea in the Hawaiian Islands is actually about four thousand feet taller than Everest. Of course, Mauna Kea begins on the bottom of the Pacific Ocean and doesn't even break sea level until it's already almost 20,000 feet high. But if you put the two side by side, Mauna Kea would actually be larger.