Crude oil is described as a finite resource. Explain how crude oil was formed and why it is considered a finite resource.

Pearson Edexcel International GCSE Chemistry (4CH1) — 4.2 Crude oil · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Crude oil is the remains of ancient biomass, mainly plankton, that was buried in mud and subjected to heat and pressure over millions of years.

It is a finite resource because it takes millions of years to form and cannot be replaced within a human timescale.

Oil is being used faster than it is formed, so once it is consumed it cannot be replaced.

Examiner tips

Use the word ‘plankton’ and ‘buried in mud’ to show understanding of formation. Show that formation takes millions of years and that usage exceeds formation. Link the two points to explain why it is finite.

Common mistakes

Confusing oil with natural gas or describing it as a renewable resource. Omitting the timescale of millions of years or the role of heat and pressure. Failing to connect the formation rate with consumption rate.

Mark scheme (4 marks)

Crude oil is the remains of an ancient biomass consisting mainly of plankton
The plankton/biomass was buried in mud (over millions of years)
Crude oil is finite because it takes millions of years to form / it cannot be replaced within a human timescale
It is being used/consumed faster than it is being formed / once used up it cannot be replaced

Key terms in this question

finite resource · crude oil