Earth and space: Earth's systems and the water and carbon cycles (grade 12) · lesson

Earth's four systems

💡 Earth's systems are the geosphere, hydrosphere, atmosphere, and biosphere, and they constantly affect each other.

The geosphere is rock and soil. The hydrosphere is all water. The atmosphere is the air. The biosphere is all living things.

Changes in one system ripple into others. Plants (biosphere) pull carbon from the air (atmosphere). Rain (hydrosphere) wears down rock (geosphere).

🧠 How to think about it

Name the system by what it is made of: rock, water, air, or life. "Bio" means life.

biosphere: all living things on Earth
geosphere: Earth's rock and soil

The water cycle

💡 Water is never used up; it changes state and moves between ocean, air, and land.

The Sun's heat makes water evaporate into vapor. Plants also release vapor from their leaves, which is called transpiration. The vapor cools and condenses into cloud droplets, falls as precipitation, and flows back to the ocean as runoff or soaks into the ground.

Water does not disappear. A puddle that dries up has evaporated into the air.

🧠 Let's work it out

Treat water like a budget.
A watershed gets 1,000 mm of rain.
600 mm evaporates or is used by plants and 150 mm soaks in, so 1,000 − 600 − 150 = 250 mm runs off.

What do you think comes next?

evaporation: liquid water turning into vapor
transpiration: plants releasing water vapor
runoff: water flowing over land

🔗 USGS: The water cycle · U.S. Geological Survey ↗

Water shapes the land

💡 Water breaks rock, dissolves it, and carries and drops sediment.

Water expands about 9% when it freezes. Ice in a crack pries the rock apart; this is frost wedging.

Water dissolves minerals, such as limestone, and can carve caves.

Fast water carries more sediment than slow water. When a river slows as it enters a lake, sand and silt settle out and build a delta.

🧠 How to think about it

For each change, find the property of water at work: expanding when frozen, dissolving, or carrying sediment when fast.

sediment: bits of rock and soil carried by water, wind, or ice
delta: land built where a river drops its sediment

The carbon cycle

💡 Most carbon is stored in rock, and volcanoes and burning fossil fuels move it into the air.

Carbonate rocks like limestone and buried remains of ancient life hold far more carbon than the air, oceans, and living things combined.

Volcanoes and burning coal and oil release that stored carbon as carbon dioxide. Photosynthesis and shell-building take carbon back out of the air and water.

The oceans absorb much of the CO₂ that people release. Dissolved CO₂ forms carbonic acid, which makes seawater more acidic.

🧠 How to think about it

For each process, ask which way carbon moves: out of rock and into the air, or out of the air and into life or rock.

ocean acidification: seawater becoming more acidic as it absorbs CO₂

Feedback loops

💡 Positive feedback makes a change grow; negative feedback pushes back against it.

Bright ice reflects sunlight. When sea ice melts, darker ocean water absorbs more sunlight, warms, and melts more ice. The change speeds itself up, so it is positive feedback.

Negative feedback works the other way: the result of a change pushes against it and steadies the system.

🧠 How to think about it

Follow the loop around once. Does the result make the first change bigger (positive) or smaller (negative)?

positive feedback: a loop that makes a change grow