Which type of rock contains oil and natural gas?
A. metamorphic rock
B. sedimentary rock
C. igneous rock
D. molten rock
B. sedimentary rock
The correct answer is B. sedimentary rock. Sedimentary rocks, formed by the deposition and consolidation of sediments, are the primary type of rocks that contain oil and natural gas. These hydrocarbons are typically found in porous spaces within sedimentary rocks, such as sandstones or limestones, where they have been trapped over long periods of time. Therefore, the main source rocks for oil and natural gas are sedimentary rocks.
The correct answer is B. sedimentary rock.
To understand why sedimentary rocks contain oil and natural gas, let's break down the process step by step:
1. Formation: Oil and natural gas are formed from the remains of plants and animals that lived millions of years ago. When these organisms died, their remains settled at the bottom of bodies of water like oceans and lakes.
2. Accumulation: Over time, layer upon layer of sediment, such as mud, sand, and clay, built up on top of the organic remains. The weight of this sediment gradually compressed the organic matter.
3. Heat and Pressure: As more layers of sediment were deposited, the temperature and pressure increased. This process, known as burial, subjected the organic matter to high heat and pressure, causing it to undergo chemical transformations.
4. Conversion: Under the intense heat and pressure, the organic matter gradually transformed into hydrocarbons, including oil and natural gas. This process, known as diagenesis, involves the breakdown of large organic molecules into smaller ones.
5. Migration: Due to their buoyancy, the newly formed oil and gas molecules tend to migrate upward through the sedimentary rock layers, seeking areas of lower pressure and permeable rock formations.
6. Trapping: To accumulate in economically recoverable quantities, oil and natural gas need to be trapped within the rock layers. This occurs when impermeable rocks, called cap rocks or seals, hold the hydrocarbons in reservoirs, preventing them from escaping to the surface.
Overall, sedimentary rocks, which are formed from the accumulation and consolidation of layered sediments, provide the ideal conditions for the formation, migration, and trapping of oil and natural gas. Therefore, they are the primary type of rock that contains oil and natural gas.