Final answer:
Shale is typically trapped between 2 km and 4 km beneath the ground, which in miles would be between 1.24 and 2.48 miles. The closest listed option and correct answer is 1 mile.
Step-by-step explanation:
The depth at which shale is trapped beneath the ground can vary considerably based on geological conditions. However, for the purposes of oil and gas extraction through methods like hydraulic fracturing, or 'fracking', it is important to note that the material must be buried under a significant thickness of rock to undergo the necessary transformations.
Based on the reference that the material must be under at least 2 km of rock to crack large organic molecules but must not go below about 4 km of rock to avoid 'overcracking' those molecules into natural gas, we can deduce that shale is typically found in the range between these depths. Using the conversion where 1 km equals approximately 0.62 miles, this range translates to between 1.24 miles and 2.48 miles. Therefore, the correct answer is 1 mile, as it falls within this range.