The geologic time scale and the great extinctions

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. 1.

   Time-scale bar. Earth formed about 4,600 million years ago, and the Precambrian ended about 541 million years ago (USGS). About what share of Earth's history is the Precambrian, by Ari's math?

   • About 1%
   • About 50%
   • About 88%
   • About 12%
2. 2.

   Time-scale bar drawn to scale. On a USGS time-scale bar drawn to scale, which part takes up most of the length, by Bo's reading?

   • The Mesozoic, with the dinosaurs
   • The Paleozoic, with early sea life
   • The Cenozoic, our own era
   • The Precambrian

3. Read this first

   Eras (USGS)

   Era	Began	Ended
   Paleozoic	541 million years ago	251.9 million years ago
   Mesozoic	251.9 million years ago	66 million years ago
   Cenozoic	66 million years ago	today

4. 3.

   The Mesozoic ran from about 251.9 to 66 million years ago (USGS). About how long did it last, by Kira's math?

   • About 318 million years
   • About 186 million years
   • About 66 million years
   • About 186 thousand years
5. 4.

   Put the three eras of the last 541 million years in order, oldest first, by Jun's reading (USGS).

   • Paleozoic, Mesozoic, Cenozoic
   • Paleozoic, Cenozoic, Mesozoic
   • Cenozoic, Mesozoic, Paleozoic
   • Mesozoic, Paleozoic, Cenozoic
6. 5.

   When does the Paleozoic end and the Mesozoic begin, by Luz's reading (USGS)?

   • About 251.9 million years ago
   • About 66 million years ago, when the Cenozoic began
   • About 541 million years ago, at the Precambrian's end
   • About 251.9 thousand years ago
7. 6.

   In a thick stack of undisturbed rock layers, where would Mesozoic layers sit, by Milo's reading?

   • Below Paleozoic layers, since the Mesozoic is older
   • Above Paleozoic layers and below Cenozoic layers
   • Mixed in at random
   • Above Cenozoic layers, at the very top

8. The Big Five (NPS)

   Extinction	About when	Species lost
   end-Ordovician	444 million years ago	86%
   Late Devonian	372 million years ago	75%
   end-Permian	251.9 million years ago	96%
   end-Triassic	200 million years ago	80%
   end-Cretaceous	66 million years ago	76%

9. 7.

   What do scientists link to the end-Ordovician extinction, by Ren's reading (NPS)?

   • The opening of the Atlantic Ocean
   • Mammals spreading across the land
   • An asteroid impact that left a crater near the equator
   • A rapid glaciation and its quick retreat
11. 8.

    What makes an extinction a mass extinction, by Tala's reading (NPS)?

    • A change of season
    • A spike in extinctions over a short span of geologic time
    • A single species becoming extinct
    • Extinctions at the usual slow rate
12. 9.

    NPS says more than 99% of species that have lived are now extinct. What does this show, by Zee's reading?

    Use the picture in question 8.

    • Extinction happened just five times
    • Extinction is a normal, ongoing part of life's history
    • Life on Earth keeps shrinking toward zero
    • Most species lasted billions of years
13. 10.

    Branching tree that narrows, then spreads out again. What usually follows a mass extinction, by Esme's reading (NPS)?

    • Life stays at low variety from then on
    • Bursts of new species among the surviving groups
    • Earth's history starts over
    • The same species return unchanged