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6th grade · Science · Unit 5 of 7

Earth's History & Fossils

Rock strata, the geologic time scale and evidence of change.

What your child practices

Practices how rock layers and the fossils in them are used to build the geologic time scale and to work out the relative ages of rocks, with examples from Minnesota, home to some of the oldest rocks in North America.

Minnesota K-12 Academic Standards benchmark: 6E.3.2.1.1; 6E.1.1.1.2 · rock layers, the geologic time scale and the relative ages of rocks

How we explain it

Children can open this short lesson before they practice.

  1. In undisturbed rock layers, the oldest layer is at the bottom.
  2. A rock that cuts across other layers is younger than the layers it cuts.
  3. Index fossils lived for a short time over a wide area, so they date layers.
  4. Earth is about 4.6 billion years old. Fossils show how life changed.

Example: A band of igneous rock cuts through three layers. Is it older or younger than them? The layers had to be there first to be cut. So the band came later. Answer: younger

Earth's History & Fossils in Minnesota

In the Minnesota K-12 Academic Standards, this is unit 5 of 7 in 6th grade Science, after Earth's Moving Surface and before Climate & Climate Change.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Minnesota Department of Education (MDE)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    A human arm, bat wing and whale flipper have similar bones. This suggests…

    • they share a common ancestor
    • they are the same species
    • it's a coincidence
    • bones come from food

  2. Question 2

    Fossils of early whales with small legs show…

    • legs grew from fins
    • whales always lived in water
    • whales are fish
    • whales descended from land animals

  3. Question 3

    Most of Earth's history took place in the…

    • Precambrian
    • Jurassic
    • Cenozoic
    • Mesozoic

  4. Question 4

    Homologous structures are…

    • made of rock
    • parts with no use
    • identical in every species
    • similar body parts from a common ancestor

  5. Question 5

    The fossil record shows that…

    • life on Earth has changed over time
    • life has never changed
    • all species lived at once
    • fossils are recent

  6. Question 6

    In a stack of rock layers that hasn't been disturbed, the oldest layer is usually…

    • at the top
    • in the middle
    • missing
    • at the bottom

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