Complex sentence: Marijuana concentrates contain extraordinarily high THC levels that could once range from 40 to 80%, up to four times stronger in THC content than high grade or top shelf marijuana, which normally measures around 20% THC levels.
Split into simpler sentences: Marijuana concentrates contain extraordinarily high THC levels that could range from 40 to 80%. This form of marijuana can be up to four times stronger in THC content than high grade or top shelf marijuana, which normally measures around 20% THC levels.