<|im_start|>system
You are a helpful AI assistant.<|im_end|>
<|im_start|>user
Why does earth have a moon?<|im_end|>
<|im_start|>assistant
There are many theories on why the Earth has a moon, but the most prevailing one is that the moon formed out of debris from a collision between ancient Earth and a Mars-sized body named Theia.<|im_end|>