The origin of crude oil
2 marks · EasyDescribe the process by which the soft parts of plants and animals in the sea are gradually converted into crude oil over time.
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The soft parts are buried by layers of sediment and changed into crude oil by heat and high pressure over millions of years.
Also accept: Organic remains are buried under sediment and converted by heat and pressure into crude oil; Sea plant and animal remains buried under sediment over millions of years form crude oil due to heat and pressure
Common mistakes: Only mentioning plants instead of both plants and animals; Ignoring heat and pressure
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Marking points
M1 · 1 mark · Mentions burial by sediment and/or that soft parts are covered up after death
M1 · 1 mark · Mentions conversion by heat and pressure over a long period (millions of years)
Worked solution
When sea plants and animals die, their soft parts sink and get buried by layers of sediment. Over millions of years, heat and high pressure convert these remains into crude oil.