Earth’s living systems sit within four interacting spheres: the atmosphere, hydrosphere, lithosphere and biosphere. This lesson covers atmospheric composition, the carbon and nitrogen cycles, and soils.
You will calculate an atmospheric composition and a soil water content. Answer the questions and collect ⭐.
Matter cycles between them through biogeochemical cycles.
The lowest layer, the troposphere, is where weather occurs; above it lies the stratosphere, which contains the ozone layer.
Dry air is approximately 78.08% nitrogen, 20.95% oxygen, 0.93% argon and about 0.04% carbon dioxide.
Carbon cycle: photosynthesis removes CO₂ from the air; respiration, decomposition and combustion return it; oceans dissolve CO₂.
Nitrogen cycle: nitrogen fixation (bacteria such as Rhizobium, and lightning) converts N₂ into ammonium; nitrification converts this to nitrates; denitrification returns N₂ to the air.
A soil is a mixture of mineral particles, organic matter (humus), water and air. Its texture depends on the proportion of sand, silt and clay. Soils develop horizons (layers) over time.
Soil water content can be found by drying a sample: water content (%) = ((wet mass − dry mass) ÷ dry mass) × 100.
Sort each process into the correct group.
Match each term to its meaning.
Spheres: Atmosphere, hydrosphere, lithosphere, biosphere
Atmosphere: Mostly N₂ (78%) and O₂ (21%); troposphere and stratosphere
Carbon cycle: Photosynthesis removes CO₂; respiration/combustion/decomposition return it
Nitrogen cycle: Fixation → nitrification → denitrification
Learn which processes add and which remove each gas. Press Finish.
You've worked through The Physical Environment. 🎉
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Next: test yourself in the Evaluate stage, then lock it in with Verify.