sentence2_structure: Fracking<>delivers<>natural gas<>from rock$$$rock<>might not otherwise be<>obtainable
sentence1: Meanwhile, Bittman discovers that extracting natural gas through fracking delays our transition to renewable energy and that fracking wells leak a large amount of methane, a powerful greenhouse gas, which makes fracked natural gas as dirty as, or dirtier than, burning coal.
sentence2: Fracking delivers natural gas from rock that might not otherwise be obtainable.
question: What delivers natural gas from rock that might not otherwise be obtainable?