Earth has layers due to its past as a molten body, which enabled differentiation of materials based on density. Heavier elements sank to form the core, while lighter elements rose to create the crust and mantle. This process occurred during Earth's early formation nearly 4.5 billion years ago. ;
Earth has layers because, during its formation, it was once molten, which allowed heavier elements to sink and lighter elements to rise, creating distinct layers. The core formed from the densest materials, while the mantle and crust were formed from lighter materials. Therefore, the correct answer to the question is C. it was once molten.
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