Answer:
Because it consists of three different layers of composition.
Step-by-step explanation:
The Earth's surface does not have a consistent shape because it is not formed by a single layer, but rather three layers of different compositions and organizations, which end up removing the consistent character from the surface and triggering a character that changes frequently.
These three layers are the lithosphere (which is solid), the hydrosphere (which is liquid) and the atmosphere (which is greasy).