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8th grade · Science · Unit 8 of 9

Earth's History & Fossils

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

What your child practices

Practices how rock layers are used to build Earth's 4.6-billion-year history, patterns in the fossil record, and anatomical and embryo evidence that living things share ancestors.

Arizona Academic Standards learning standard: 8.E1U1.6 · the relative ages of rock layers and the fossils in them

How we explain it

Children can open this short lesson before they practice.

  1. Rock layers and fossils order Earth’s 4.6-billion-year history; lower layers are older.
  2. Most of that history is the Precambrian. We live in the Cenozoic Era.
  3. Homologous structures show that living things share ancestors.

Example: In which era do we live today? The eras go Paleozoic, Mesozoic, Cenozoic. The latest is the Cenozoic. Answer: the Cenozoic Era

Earth's History & Fossils in Arizona

In the Arizona Academic Standards, this is unit 8 of 9 in 8th grade Science, after Natural Selection and before Resources & Hazards.

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: Arizona Department of Education

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

    The fossil record shows that…

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

  2. Question 2

    Dinosaurs (other than birds) went extinct about…

    • 1 billion years ago
    • last century
    • 10,000 years ago
    • 66 million years ago

  3. Question 3

    Homologous structures are…

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

  4. Question 4

    We live in the…

    • Cenozoic Era
    • Precambrian
    • Paleozoic Era
    • Mesozoic Era

  5. Question 5

    Earth is about how old?

    • 1 million years
    • 4.6 billion years
    • 6000 years
    • 100 years

  6. Question 6

    Vestigial structures, like the human tailbone, are…

    • new organs
    • reduced parts that once had a use in ancestors
    • parts from food
    • always harmful

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