Lesson 6

6

The Story of Rocks

What can a rock tell us about the history of Earth?

Rocks preserve evidence of Earth's past and continue to change through the rock cycle. The lesson covers how igneous, sedimentary, and metamorphic rocks form, along with the effects of heat, pressure, weathering, and erosion.

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Key Ideas

  • Igneous rocks form when magma or lava cools and solidifies.
  • Sedimentary rocks form from layers of sand, mud, and particles compressed over millions of years. They often contain fossils.
  • Metamorphic rocks form when existing rocks are changed by extreme heat and pressure deep underground.
  • The rock cycle shows how all three types can transform into each other over time.
  • Erosion constantly breaks rocks down and carries material to new places.

Spines

Vocabulary

  • Igneous Rock: Rock formed when magma or lava cools; examples include granite and basalt.
  • Sedimentary Rock: Rock formed when layers of particles are compressed over time; often contains fossils.
  • Metamorphic Rock: Rock changed by extreme heat and pressure underground, altering its structure without melting.
  • Rock Cycle: The slow, ongoing process by which rocks are created, broken down, and transformed from one type to another.
  • Erosion: The wearing away and movement of rock and soil by wind, water, ice, or gravity.
  • Fossil: The preserved remains or traces of ancient life found in sedimentary rock.

Discussion Questions

  1. What are the three types of rocks?
    Sample Answer: Igneous, sedimentary, and metamorphic.
  2. Where do igneous rocks come from?
    Sample Answer: They form when hot melted rock called magma or lava cools and hardens.
  3. How are sedimentary rocks made?
    Sample Answer: Layers of sediment, like sand, mud, and tiny shells, get pressed together over a very long time.
  4. Why do sedimentary rocks often contain fossils?
    Sample Answer: When organisms die near water, they can get buried quickly by layers of sediment before decomposing, leaving behind impressions or bones.

Digging Deeper

  1. How does the rock cycle show that rocks are always changing?
    Sample Answer: Heat, pressure, and weathering can change any type of rock into another type over millions of years. It's a slow, continuous cycle.