Complex sentence: Unlike, the other three states of solid, liquid, and gas, plasma does not freely exist on the Earth, and can only be artificially generated by heating neutral gases or by subjecting that gas to a strong electromagnetic field.
Split into simpler sentences: Unlike, the other three states of solid, liquid, and gas, plasma does not freely exist on the Earth. Plasma can be generated by heating neutral gases or by subjecting gas to a strong electromagnetic field.