The origin of crude oil

3 marks · Normal

Crude oil takes millions of years to form. Suppose a layer of organic material is buried under sediment for 60 million years. If the process began 350 million years ago, calculate how many years ago the crude oil finished forming. Show your working.

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Show answer

290 million years ago (±0)

Common mistakes: Adding instead of subtracting

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Marking points

M1 · 1 mark · States the correct calculation method (subtracts time taken from start time). (follow-through)

M2 · 1 mark · Shows clear step(s) of working.

A1 · 1 mark · Arrives at correct answer: 350 − 60 = 290 million years ago. (follow-through)

Worked solution

Start time = 350 million years ago

Time taken to form crude oil = 60 million years