Earth Systems and Resources

Earth's crust is broken into plates 板块 that slowly move on the mantle – plate tectonics 板块构造. At divergent boundaries plates spread apart (new crust); at convergent they collide (mountains, volcanoes, earthquakes); at transform they slide past (earthquakes). Boundaries create hazards but also volcanic soils and mineral resources.

A volcano erupting at a plate boundary in Iceland. Molten rock rising between spreading plates builds new crust

Soil 土壤 forms slowly as rock weathers 风化 and organic matter builds up. Erosion 侵蚀 is the removal of soil by wind and water, sped up by removing vegetation (farming, deforestation, overgrazing). Because soil forms so slowly, erosion faster than formation depletes a vital resource.

Soil is a mix of sand, silt, and clay (its texture 质地), plus organic matter, water, and air, layered in horizons 土层. Texture controls porosity 孔隙度 and permeability 渗透性 – how well soil holds water and nutrients. Loam (a balanced mix) is best for plants.

A pit dug through soil shows its horizons: dark organic topsoil on top, then paler mineral layers, over broken rock (tape for scale)

The atmosphere 大气层 is layered: the troposphere 对流层 (weather, where we live), the stratosphere 平流层 (holding the ozone layer), and higher layers. It is mostly nitrogen and oxygen, with trace gases (including greenhouse gases) that regulate temperature.

Clean dry air is about 78% nitrogen, 21% oxygen, and 1% other gases

Uneven solar heating drives global wind patterns 全球风带. Warm air rises at the equator and sinks at about 30°, creating convection cells 对流环流 (Hadley, Ferrel, polar) and prevailing winds (trade winds, westerlies). The spinning Earth deflects winds – the Coriolis effect 科里奥利效应 – shaping weather and climate.

Three circulation cells per hemisphere set the prevailing surface winds

A watershed 流域 is all the land that drains to a common body of water. Everything that happens on the land – farming, paving, pollution – affects the water it drains into, so watersheds are key units for managing water quality.

Seasons come from Earth's tilted axis (about 23.5°), not its distance from the Sun. The hemisphere tilted toward the Sun gets more direct sunlight and longer days (summer). The tilt also makes the tropics warm year-round and the poles cold.

The tilt of the Earth's axis causes the seasons

Geography shapes climate: latitude (sunlight angle), elevation (cooler with height), proximity to oceans (moderating temperature), and mountains creating a rain shadow 雨影 (wet windward side, dry leeward side). These factors decide which biome forms where.

El Niño 厄尔尼诺 and La Niña 拉尼娜 are periodic shifts in Pacific Ocean temperatures and winds. El Niño (warm eastern Pacific) and La Niña (cool eastern Pacific) alter rainfall, storms, and fisheries worldwide – for example, floods in some regions and droughts in others.

Worked example. A tectonic plate moves 5 cm per year. How far does it travel in 1 million years? $5\ \text{cm/yr}\times 10^{6}\ \text{yr}=5\times10^{6}\ \text{cm}=50\ \text{km}$. A tiny yearly motion adds up to ocean-basin-scale distances over geologic time — the same slow rate that opens oceans and builds mountain ranges.

• Seasons come from the Earth's tilt, not its distance from the Sun.
• Soil forms very slowly, so erosion faster than formation permanently depletes it; know soil texture (sand/silt/clay) and horizons.
• Explain global wind patterns from uneven heating + the Coriolis effect, and a rain shadow (wet windward, dry leeward).
• Name the atmospheric layers (troposphere = weather, stratosphere = ozone) and air composition (~78% N₂, 21% O₂).
• El Niño / La Niña are Pacific temperature shifts that change rainfall worldwide.