Earth sciences and environment: soil, climate, ecology and resources
Earth sciences and environment tests how soil, climate, organisms and resources interact, with a strong Mediterranean and Lebanese field context. Expect texture and water-holding calculations, climate classification, trophic reasoning and land-management judgments.
Core rules
- Soil: texture (sand, silt, clay) is read on a texture triangle; structure describes aggregation. Bulk density = oven-dry mass / bulk volume; porosity = 1 − bulk density/particle density. Cation exchange capacity (CEC) measures retained exchangeable cations, reported in cmol(+)/kg. Field capacity is water held after drainage; permanent wilting point is where plants cannot extract water.
- Climate: the Mediterranean regime has mild wet winters and hot dry summers. Albedo controls reflected radiation; the environmental lapse rate is about 6.5 °C per km; greenhouse gases absorb outgoing infrared radiation.
- Ecology: energy decreases up trophic levels, often summarized by a roughly 10% transfer; carrying capacity limits population growth; succession changes community composition over time; nitrogen and phosphorus cycles control productivity.
- Resources: erosion, salinization and overgrazing degrade land; irrigation without drainage raises water tables and concentrates salts.
Worked example
A soil sample has oven-dry mass 150 g and bulk volume 100 cm³; particle density is 2.65 g/cm³. Find bulk density and porosity. Bulk density = 150/100 = 1.50 g/cm³. Porosity = 1 − 1.50/2.65 = 1 − 0.566 = 0.434, about 43%. Reasoning: porosity is pore volume fraction; it is not the same as water content, and it uses particle density, not bulk density, in the denominator.
Traps that cost marks
- Confusing soil texture with structure.
- Reporting porosity as a mass percentage.
- Reversing the energy flow in trophic pyramids.
- Treating CEC as total salt content rather than exchange capacity.
- Assuming all irrigation improves saline soils.