Complex sentence: Mainstream scientists argue that the theory contradicts the empirical evidence and well established theories, which state that the Earth's magnetic field has varied in intensity, and even reversed in polarity, numerous times in the earth's history.
Split into simpler sentences: Mainstream scientists argue that the theory contradicts the empirical evidence and well established theories. The Earth's magnetic field has varied in intensity, and even reversed in polarity, numerous times in the earth's history.