Earth as a System: Energy, Matter, and Life

The Sun powers the Earth system: how sunlight is reflected and absorbed, why land and sea heat differently, the cycles of matter, and human impact.

Key ideas

About 30% of incoming sunlight is reflected to space; the rest is absorbed by the atmosphere and the surface.
Albedo is the fraction of light a surface reflects: high for snow, low for oceans and dark roads.
Water has a high specific heat, so land heats and cools faster than the sea: sea breezes by day, land breezes by night.
Matter cycles: water (evaporation, transpiration, condensation, precipitation), carbon and oxygen (photosynthesis, respiration, burning), nitrogen (fixation, nitrification, denitrification).
Greenhouse gases trap heat; burning fossil fuels and cutting forests add carbon dioxide and warm the climate.
In a food chain only about 10% of the energy passes to the next level.

Heat needed	Q = m × c × ΔT (water c = 4200 J/kg °C)
Absorbed sunlight	incoming × (100% − albedo)
Rainfall	1 mm of rain on 1 m² = 1 litre
10% rule	energy at the next level = energy × 0.1

Saying the breeze blows from the hotter side: air flows towards the hotter land, where warm air rises.
Mixing up nitrogen fixation (gas to compounds) and denitrification (compounds to gas).
Confusing the greenhouse effect (natural) with global warming (the extra rise people cause).

The plants in a forest capture 7,000 kJ of energy. Using the 10% rule, how much reaches the top carnivores (third consumers)?

Working: 10% passes to each next level: 7,000 → 700 → 70 → 7 kJ; the herbivores (e.g. deer) get 700 kJ

Answer: 7 kJ