Origins of petroleum — theory check: Which theory for the origin of petroleum fails to account for the presence of nitrogen and sulphur compounds commonly observed in crude oil?

Introduction / Context: Crude oils contain heteroatoms such as nitrogen and sulphur bound within complex molecules (e.g., pyridines, porphyrins, thiophenes). A sound origin theory should plausibly explain how such heteroatoms entered and persisted in the organic matrix during geological transformation.

Given Data / Assumptions:

• Modern and Engler theories are organic-origin models.
• Carbide theory is an inorganic-origin proposal (e.g., metal carbides reacting with water to form hydrocarbons).
• Observed crude composition includes N and S species of biological provenance.

Concept / Approach: Organic origin models derive petroleum from biological matter (plankton, algae) that naturally contains nitrogen and sulphur in biomolecules; diagenesis and catagenesis concentrate and transform these into the heteroatom species found in crude. The inorganic carbide theory does not naturally account for these heteroatoms, making it inconsistent with the compositional evidence.

Step-by-Step Solution:

Verification / Alternative check: Biomarkers such as porphyrins (linked to chlorophyll/hemoproteins) argue strongly for organic origin and explain nitrogen presence; sulphur arises from biological sulphur cycles and sulphate-reducing environments.

Why Other Options Are Wrong:

Common Pitfalls: Assuming all origin theories are equally capable of explaining composition; inorganic pathways struggle with ubiquitous biogenic markers.

Final Answer: Carbide (inorganic) theory