How life and Earth have changed each other
Grade 9 Science Worksheet
Circle the best answer.
The ozone layer absorbs 98% of UV light (example data). If it thins until it absorbs 96%, by what factor does the UV reaching the ground change for Bo?
- It rises by half, from 2% to 3% of the UV
- It rises 2%, from 98% to 100% of the UV
- It doubles, from 2% to 4% of the UV
- It barely changes, since 98% and 96% are close
Read this first
Events (approximate, millions of years ago)
Event Millions of years ago Microbes raise oxygen in the air 2,400 Land plants spread 470 Jun links the events. Which chain fits the table, and how long was the gap between the two?
- Microbes raise oxygen, and land plants spread about 470 million years later
- Land plants spread, and microbes raise oxygen about 1,930 million years later
- Microbes raise oxygen, and land plants spread about 2,870 million years later
- Microbes raise oxygen, and land plants spread about 1,930 million years later
A loop (example)
Step Result 1 more oxygen thickens the ozone layer 2 a thicker ozone layer lets more plants grow on land 3 more plants release more oxygen Luz follows steps 1 to 3 and returns to step 1. Which description of the loop is correct?
- No loop: life changes the air once and the air does not change life
- A reinforcing loop: more oxygen leads to more plants, which add more oxygen
- A damping loop: more oxygen leads to more plants, which remove oxygen
- A damping loop: a thicker ozone layer slows plant growth, which lowers oxygen
A reef grows 5 mm a year while sea level rises 12 mm a year (example data). What does Milo predict for the reef?
- It falls behind by 7 mm a year and drowns below the sunlit water
- It keeps up easily, since it grows faster than the sea rises
- It falls behind by 17 mm a year and drowns below the sunlit water
- It grows above the sea surface, since coral can outgrow any sea level
A volcanic island sinks 0.03 mm a year for 30 million years while its reef keeps up (example data). How thick is the limestone cap, by Noah's math?
- About 9,000 m
- About 900 m
- About 900 km
- About 90 m
Card
CaSiO₃ + CO₂ gives CaCO₃ + SiO₂ when rock weathers and shells later lock up the carbon. CaSiO₃ is 116 g per mole; CO₂ is 44 g per mole.
Ari weathers 1 tonne of CaSiO₃ rock and buries the carbon as limestone. How much CO₂ is removed?
- About 0.12 tonne
- About 1 tonne
- About 0.38 tonne
- About 2.6 tonnes
The weathering loop (example)
Step Result 1 warmer climate gives more rain and faster weathering 2 faster weathering pulls more CO₂ from the air 3 less CO₂ cools the climate Tala follows the loop back to step 1. Why does it help keep Earth's climate from running away?
- Weathering does not depend on climate, so there is no loop
- Each warming causes more weathering and CO₂ removal, which cools the climate and works against the warming
- Each warming causes more weathering, which adds CO₂ and warms the climate further
- Each warming slows weathering, so CO₂ builds up and cools the climate
Weathering of similar rock (example data)
Plot Weathering (mm per year) Bare rock 0.01 Rock under a forest 0.04 Zee compares the plots. What do the data show, and what follows for CO₂ over long times?
- Roots speed weathering 3 times, so more CO₂ is pulled into rock
- Roots slow weathering to a fourth, so less CO₂ is pulled into rock
- Roots have no effect on weathering, so CO₂ stays the same
- Roots speed weathering 4 times, so more CO₂ is pulled into rock
Soil holds 15% of its volume as water when wet. Bare rock holds none. Esme compares 30 cm of wet soil with bare rock. How much rain can the soil store, and why does it help plants?
- About 450 mm, which keeps roots supplied between rains
- About 4.5 mm, which keeps roots supplied between rains
- About 45 mm, which keeps roots supplied between rains
- About 45 mm, but just because the rock beneath holds it
Card
1 Dobson unit (DU) of ozone is a layer 0.01 mm thick at the ground. An ozone hole is a column of under 220 DU.
Ren brings a 220 DU column of ozone down to ground level. How thick is the layer?
- About 2.2 m
- About 22 mm
- About 0.22 mm
- About 2.2 mm