Science Fenns K-5Grades K to 5
A cross-section picture of ancient swamp plants and sea life buried under layers of mud, with a modern oil pump far above.

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How Fossil Fuels Form

Ancient life, pressure and time.

Lesson 29 of 41

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Before we start

Today’s story

How Fossil Fuels Form

Millions of years ago, swamps and shallow seas were full of life. Plants grew in the swamps. Tiny sea creatures lived and died in the water. When they died, their remains sank to the bottom.

Mud and sand piled on top of the remains. The weight pressed down and heat from deep in Earth added more. Over millions of years the remains changed. Plant matter became coal. Sea life became oil and natural gas.

These are called fossil fuels. They hold energy that came from the Sun long ago, stored by living things. Here are the steps.

See it

Five steps. Every time.

    Hands on

    Squeeze It Model

    25 minutes · Do this with a grown-up nearby

    You need

    • modeling clay in several colors
    • a plastic cutting board
    • a heavy book
    • wax paper
    • a ruler

    Do this

    1. Roll a thin green layer of clay. It is the ancient plants.
    2. Lay a thin layer of tan clay on top. It is sand and mud.
    3. Add more layers of different colors.
    4. Cover with wax paper and set the book on top.
    5. Press down hard for a minute and lift.
    6. Measure the stack before and after.
    Write or draw: Draw the stack before and after. Write how the thickness changed.

    Watch for: The layers get thinner and denser. Real pressure pushes out water and changes the remains.

    Safety: Wash hands after using clay. Do not eat the clay.

    Same every time

    Three rules

    Rule 1Fossil fuels start as living things.

    Their energy first came from the Sun.

    Rule 2It takes millions of years.

    We use them far faster than they form.

    Rule 3They are nonrenewable.

    Once used up, they are gone for a very long time.

    Grandpa Fenn’s notebook

    Say it like a scientist

    fossil fuel
    Coal, oil or natural gas made from ancient living things.
    nonrenewable
    Cannot be replaced in a human lifetime.
    pressure
    A push that squeezes on something.
    decay
    When dead plants and animals rot and break down.

    Poppy’s quiz

    Six questions

    Tap an answer. Green means right. You will see why.

    Talk about it

    Say it out loud

    • What evidence shows that oil came from living things?
    • Have you seen a pump jack or gas truck near you? What do you think the fuel is used for?
    Did you know

    Natural gas, the kind that heats many Texas homes, usually forms with oil deep underground, so wells often bring up both.

    Someone who does this

    A petroleum engineer plans how to find and pump oil and gas.

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