Final answer:
The small bodies from which planets formed are known as planetesimals, which grew by accretion to become protoplanets.
Step-by-step explanation:
Small bodies from which the planets formed are called planetesimals. These small chunks of solid matter, composed of ice and dust particles, were critical in the early stages of the solar system's formation. Planetesimals that were large enough could attract other planetesimals gravitationally, growing by a process called accretion. This process ultimately resulted in the formation of protoplanets, which are essentially baby planets not yet fully developed into the massive bodies we know today as the planets in our solar system.