How we know past climates: ice cores, tree rings, sediments

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Why are yearly layers deep in an ice sheet much thinner than near the top, by Esme's reading (NASA)?

   • Snow fell at one fixed rate for many years, then stopped
   • Each deep layer holds one day
   • The weight above squeezes deep snow into thin ice layers
   • The drill stretches the shallow ice

2. Read this first

   Use this

   Table, Ice-core CO₂ and Antarctic temperature (NOAA NCEI), with columns About how long ago, CO₂ in trapped air (ppm), Temperature vs last 1,000 years: 20,000 years, 194, −9.4 °C; 128,000 years, 276, +3.4 °C; 140,000 years, 193, −9.1 °C. Note: CO₂: Antarctic composite (Bereiter et al. 2015); temperature: EPICA Dome C (Jouzel et al. 2007); values rounded.

3. 2.

   Using the ice-core table, how much higher was CO₂ about 128,000 years ago, a warm time, than about 140,000 years ago, a cold time, by Jun's math?

   • Thermometer readings from that time, about 83 °C
   • About 469 ppm
   • About 8.3 ppm
   • About 83 ppm

4. Ring widths of a rain-sensitive tree (model data)

   Year	Ring width
   1901	3 mm
   1902	1 mm
   1903	4 mm

5. 3.

   Using the ring-width table for a rain-sensitive tree, which year was likely wettest, by Kira's reading?

   • 1903
   • 1902
   • They were equally wet
   • 1901
6. 4.

   A log's last 10 rings match a living tree's rings for 1650 to 1659 (model data). The log has 300 rings. In what year did its first ring form, by Luz's math?

   • 1359
   • 1360
   • 1959
   • 1350
7. 5.

   Why do scientists core many trees, not one, by Milo's reading (NOAA)?

   • Coring many trees makes the rings wider
   • Each tree grows a different number of rings a year
   • One tree's rings settle a region's climate
   • More samples make it surer that ring changes reflect climate
8. 6.

   Light oxygen moving from the sea into an ice sheet. Fossil shells in a sediment core hold more heavy oxygen than the standard (NASA). What does that suggest, by Pia's reading?

   • More ice held light oxygen, so it was a cold, icy time
   • Heavy oxygen means warm, fresh water
   • The trees grew wider rings
   • The ice sheets were melting fast
9. 7.

   Several proxy records lined up on one timeline. NASA: light oxygen in local sea water can also mean heavy rain nearby. Why compare several proxies, by Ren's reading?

   • One signal can have several causes, so others help confirm it
   • Each proxy gives the exact temperature by itself
   • Proxies agree in each case
   • Rain makes oxygen heavier

10. Use this

    Ice, a tree ring, a sediment layer and a pollen grain in a row.

11. 8.

    NOAA: pack rats gather plants within about 100 m, and their middens last tens of thousands of years. A midden full of drought-tolerant plants suggests what, by Tala's reading?

    • A wet climate when it formed
    • Thermometer data from that time
    • A pack rat carried it 100 km
    • A dry climate when it formed
12. 9.

    Pollen grains in lake layers show which plants grew nearby (NOAA). What does a shift from spruce pollen to oak pollen, moving up a core, suggest, by Zee's reading?

    • The local climate grew warmer over time
    • The lake dried out in a day
    • The local climate grew colder over time
    • The pollen grains changed shape
13. 10.

    Several proxy records lined up on one timeline. NOAA: grape-harvest dates were used to reconstruct Paris summers from 1370 to 1879. About how many years is that span, by Ari's math?

    • About 510 years
    • About 51 years
    • About 5,090 years
    • About 3,249 years