Earth and space: resources, hazards, and sustainability (grade 12) · lesson

Renewable and limited resources

💡 A resource lasts only if it is replaced as fast as it is used.

Wind and sunlight are renewable: nature replaces them constantly. Coal, oil, natural gas, and uranium are not replaced on a human time scale.

Groundwater in an aquifer refills slowly from rain. If pumping is faster than refilling, the water table drops and wells go dry.

🧠 Let's work it out

Find the net change, then divide.
Pump 50 million m³ a year and refill 20: the net loss is 30 per year.
900 ÷ 30 = 30 years until a 900 million m³ aquifer runs out.

What do you think comes next?

renewable: replaced naturally as fast as it is used
aquifer: underground rock or sand that holds water

🔗 USGS: Groundwater decline and depletion · U.S. Geological Survey ↗

Living with natural hazards

💡 People settle near hazards for the resources there, and smart planning lowers the risk.

Many cities grew along rivers because rivers supply water, fertile soil, and travel routes, even though they flood.

Coastal wetlands and dunes slow waves and soak up water, lowering storm-surge flooding. Paving them removes that protection.

Climate models predict long-term trends. A region expecting hotter, drier years can switch to crops that need less water and store water in wet years.

🧠 How to think about it

For any plan, ask: does it give water somewhere to go, slow it down, or prepare for less of it? Plans that do the opposite raise the risk.

storm surge: a rise in sea level pushed ashore by a storm

🔗 Khan Academy: Earth and society · Khan Academy (free) ↗

Protecting land and water

💡 Letting water soak in and keeping soil covered protects rivers and farmland.

Pavement makes rain rush off and carry pollution into rivers. Rain gardens and surfaces that let water through help it soak in and get filtered.

Cover crops and windbreak trees hold soil in place. Bare fields and plowing straight downhill let soil wash or blow away.

Recycling metal means less new mining. Restoring land after mining helps habitats recover.

🧠 How to think about it

Ask whether each choice slows water and holds soil, or speeds water and exposes soil.

cover crop: a crop planted to protect the soil between harvests

Trade-offs

💡 Every choice gives up something to gain something else, so compare both sides with numbers.

A wind farm costs more to build than a coal plant, but it needs no fuel and makes no smoke. Paying more now to save fuel and keep air cleaner later is a trade-off.

Numbers make trade-offs clearer. A percent shows how much a solution covers.

🧠 Let's work it out

Solar panels make 4,800 kWh and a family uses 12,000 kWh.

4,800 ÷ 12,000 = 0.40, or 40%.
The panels cover part of the need, not all of it.

What do you think comes next?

trade-off: giving up one thing to gain another