Notes
Plate tectonics
- Divergent boundaries: plates move apart (mid-ocean ridges, rift valleys, new crust).
- Convergent boundaries: plates collide. Ocean-continent makes subduction zones, trenches and volcanoes; continent-continent makes mountains (the Himalayas).
- Transform boundaries: plates slide past each other, causing earthquakes (the San Andreas Fault).
- Earthquakes and volcanoes cluster along plate boundaries, like the Ring of Fire.
Soil
- Soil horizons: O (organic litter), A (topsoil, humus), B (subsoil, minerals), C (weathered parent rock).
- Soil forms from weathering of parent material, plus organisms, climate, topography and time.
- Texture: sand, silt, clay. Sand drains fast (high permeability); clay holds water and drains slowly. Loam (a mix) is best for most plants.
- Erosion is caused by wind and water; plant roots hold soil.
Atmosphere
- Layers from the ground up: troposphere (weather, where we live), stratosphere (ozone layer), mesosphere, thermosphere, exosphere.
- The atmosphere is about 78% $\mathrm{N_2}$, 21% $\mathrm{O_2}$, about 0.9% argon, and small amounts of $\mathrm{CO_2}$ and water vapor.
Global circulation, climate and weather
- Uneven solar heating (the equator gets the most direct sunlight) drives air circulation in Hadley cells. Warm, moist air rises at the equator (rainforests); dry air sinks around 30° latitude (deserts).
- The Coriolis effect deflects winds because Earth rotates.
- Rain shadow effect: moist air rises up the windward side of mountains, cools and drops rain; the leeward side is dry.
- Watersheds are land areas that drain into one body of water.
- El Niño: trade winds weaken, warm water spreads east across the Pacific, upwelling off South America decreases, and global weather shifts. La Niña is the opposite.
Practice
Two continental plates collide and push the crust up.
The O horizon above it is mostly leaf litter; B is subsoil; C is weathered parent rock.
Large particles leave large pore spaces for water to drain.
Stratospheric ozone absorbs UV radiation.
Air that dropped its moisture at the equator descends near 30°.
That's the rain shadow effect.
Weaker trade winds reduce cold, nutrient-rich upwelling.
About 78% of the atmosphere is $\mathrm{N_2}$.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A town is located on the east side of a mountain range. Winds usually blow from west to east.
(a) Predict whether the town is wet or dry. Explain.
Show the answer and scoring guide
Dry. Moist air rises up the west (windward) side, cools, and drops most of its water as rain. When it comes down the east side, it warms and is dry.
Check off the points you earned:
(b) Describe one way the soil on the windward side might differ from the soil on the leeward side.
Show the answer and scoring guide
The windward side may have thicker, more organic soil from more plant growth, but also more leaching of nutrients because of heavy rain.
Check off the points you earned:
(c) Identify the layer of the atmosphere where this weather happens.
Show the answer and scoring guide
The troposphere.
Check off the points you earned: