Here are a few questions related to this discussion of the Earth, a brief discussion for each question, and some links to places to read more. The geology there is so much simpler there than on the continents that it became possible to see how the sea-floor might have formed. After an earthquake, waves travel out through the ground and deep underground like ripples on a pond. Close by, these waves are felt as alarming ground shaking. Further away they are barely perceptible but can be measured by sensitive seimsographs.
Convection occurs when a hot fluid is heated from below or cooled from above.
In a Lava Lamp, the light bulb in the base heats up oil at the bottom of the glass tube. This oil expands very slightly as it warms up and becomes just light enough to float to the top of the tube where it cools slightly, gets heavier again and sinks. Convection is ubiquitous. It occurs in stars, in giant gassy planets, in the Earth, in the atmosphere, in the ocean, in a room with a heater. Convection in the mantles of other planets is probably provided they have sufficient heat energy within them.