Home / Courses / Environmental Science / Unit 3

Environmental Science Unit 3: Earth systems and resources

Earth's physical systems, from tectonic plates to soil and the atmosphere, set the stage for life and human resource use.

Covers: Plate tectonics, soil formation and properties, atmosphere layers, global wind patterns, watersheds, El Niño

Study guide

Earth's surface is shaped by plate tectonics. The lithosphere is broken into plates that move on the softer asthenosphere, driven by mantle convection. At divergent boundaries plates move apart, forming mid-ocean ridges and rift valleys. At convergent boundaries they collide, causing subduction, volcanoes, trenches and mountains. At transform boundaries they slide past each other, causing earthquakes, as along the San Andreas Fault.

Soil forms from weathered parent rock, organic matter, water and air over long periods. Soil profiles have layers called horizons: O (organic), A (topsoil), B (subsoil, where minerals accumulate) and C (parent material). Soil texture depends on its mix of sand, silt and clay, which affects water holding and drainage; loam is ideal for farming. Soil can be lost through erosion and degraded by overuse.

The atmosphere has layers: the troposphere (weather happens here), the stratosphere (contains the ozone layer, which absorbs UV), the mesosphere and the thermosphere. It is about 78% nitrogen and 21% oxygen.

Global wind patterns come from uneven heating of Earth's surface and the Coriolis effect from Earth's rotation. Warm air rises at the equator and sinks around 30° latitude, forming convection cells that create trade winds, westerlies and the world's major deserts. Ocean currents redistribute heat as well.

A watershed is all the land that drains into one body of water. El Niño (ENSO) occurs when Pacific trade winds weaken and warm water spreads east, disrupting upwelling and changing weather worldwide; La Niña is the opposite phase.

During El Niño, surface water in the eastern Pacific is warmer than normal, upwelling off South America weakens, and rainfall increases along the west coast of the Americas while Indonesia and Australia get drier. La Niña is the reverse: stronger trade winds, cooler eastern Pacific water and stronger upwelling, with wetter conditions in the western Pacific and drier conditions in the southern United States. Upwelling brings cold, nutrient-rich deep water to the surface, supporting plankton and some of the world's most productive fisheries. Anything that weakens upwelling, such as El Niño, lowers that productivity.

Key ideas

• Plate boundaries: divergent, convergent and transform.
• Soil forms from weathered parent material plus organic matter; horizons are O, A, B, C.
• The troposphere holds weather; the stratosphere holds the ozone layer.
• Uneven solar heating drives global winds and ocean currents.
• El Niño weakens trade winds and warms the eastern Pacific.

Formulas and rules

Common mistakes

• Putting the ozone layer in the troposphere.
• Confusing weathering (breaking rock) with erosion (moving it).

Words to know

Stratosphere

The atmosphere layer that contains the ozone layer.

A horizon

The topsoil layer.

Transform boundary

Plates slide past each other (San Andreas Fault).

Watershed

Land area that drains into one body of water.

El Niño

Weakened trade winds and a warmer eastern Pacific.

Soil horizons

O (organic), A (topsoil), B (subsoil), C (parent material).

Layers of the atmosphere

Troposphere → stratosphere → mesosphere → thermosphere.

Lithosphere

Earth's rigid crust and upper mantle, broken into plates.

Convergent boundary

Plates collide: subduction, volcanoes, mountains.

Divergent boundary

Plates move apart: ridges and rift valleys.

Soil texture

The mix of sand, silt and clay.

Loam

Balanced soil ideal for farming.

Troposphere

The lowest atmosphere layer, where weather happens.

Coriolis effect

Earth's rotation deflects winds and currents.

Hadley cell

Air rises at the equator and sinks near 30°, creating deserts.

Upwelling

Cold, nutrient-rich water rising to the surface.

La Niña

Stronger trade winds and a cooler eastern Pacific; the opposite of El Niño.

Soil formation

Weathering of parent rock plus organic matter, water and air over long periods.

Global wind patterns

Trade winds, westerlies and polar easterlies from convection cells and the Coriolis effect.

Sample practice questions

5 more questions like these, from level 1 to 5, are in the practice set.