- Fossil fuels / fossils forming occurs over a period of 300000000 years which is considered a very long time to a human
- Fossil fuels / fossils are formed from dead organisms over time
- So, fossil fuels are formed from dead organisms over a very long period of time

- Fossil fuels are formed from dead organisms over a very long period of time
- If something formed from something else over a very long period of time then that something else existed a very long time ago
- So, fossil fuels are formed from dead organisms from a very long time ago

- Fossil fuels are formed from dead organisms from a very long time ago
- Prehistoric means a very long time ago
- Hence, fossil fuels are formed from dead prehistoric organisms

- If a living thing dies then that living thing is dead
- A living thing is an organism
- So, if an organism dies then that organism is dead

- If an organism dies then that organism is dead
- Dead organisms decay
- Therefore, if an organism dies then that organism is dead and decays

- Fossil fuels are formed from dead prehistoric organisms
- If an organism dies then that organism is dead and decays
- So, fossil fuels are formed from prehistoric organisms dying and decaying

- Fossil fuels are formed from prehistoric organisms dying and decaying
- An animal is a kind of organism
- So, fossil fuels are formed from prehistoric animals dying and decaying

- Fossil fuels are formed from prehistoric animals dying and decaying
- Oil is a kind of fossil fuel
- Therefore, oil is formed from prehistoric animals dying and decaying

Therefore, oil is formed from prehistoric animals dying and decaying
[Question]When prehistoric animals died and their soft parts decayed, which product was formed?
[Context]- If something formed from something else over a very long period of time then that something else existed a very long time ago 
- Prehistoric means a very long time ago 
- If a living thing dies then that living thing is dead 
- Fossil fuels / fossils forming occurs over a period of 300000000 years which is considered a very long time to a human 
- Oil is a kind of fossil fuel 
- A living thing is an organism 
- An animal is a kind of organism 
- Dead organisms decay 
- Fossil fuels / fossils are formed from dead organisms over time