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IB DP ESS — Topic 5: Land | SL & HL | Paper 1 & Paper 2
🎯 Learning Intentions By the end of this note, you will be able to:
- Define soil, soil organic matter, and soil biodiversity using IB-aligned ESS terminology.
- Explain how soil functions as a critical component of terrestrial ecosystems, including its roles in nutrient cycling, water regulation, and primary production support.
- Describe the diversity of organisms found in soil and their roles in decomposition, nutrient cycling, and soil structure formation.
- Explain how soil acts as both a carbon sink and a carbon source, and the conditions under which each role dominates.
- Analyse the impacts of land-use change, agriculture, and climate change on soil carbon stocks and soil biodiversity, using ESS analysis parameters including scale, sustainability, and trade-offs.
- Evaluate the effectiveness of soil conservation strategies — including no-till farming, cover cropping, and rewilding — in maintaining soil functions and carbon sequestration.
- Discuss contrasting worldviews (ecocentric, technocentric, anthropocentric) in relation to soil management and the valuation of soil ecosystem services.
Real-World Context & Relevance
In 2015, the United Nations Food and Agriculture Organization published a landmark report — Status of the World's Soil Resources — warning that approximately 33% of global soils are already degraded, and that at current rates of loss, the world's topsoil could be functionally exhausted within 60 years. This is not a distant abstraction: in the American Midwest, the Dust Bowl of the 1930s stripped millions of hectares of topsoil from the Great Plains, triggering one of the worst agricultural and humanitarian disasters in US history. The same dynamics are playing out today across sub-Saharan Africa, South Asia, and Central Asia, where soil erosion, salinisation, and compaction are reducing agricultural yields at a time when global food demand is rising.
Yet soil is far more than a medium for growing crops. A single teaspoon of healthy forest soil contains more microorganisms than there are people on Earth — bacteria, fungi, protozoa, nematodes, and archaea forming one of the most complex and least understood ecosystems on the planet. Globally, soils store approximately 1,500–2,400 Gt of organic carbon — roughly twice the amount held in the atmosphere and three times the amount stored in all living vegetation combined (IPCC, Climate Change and Land , 2019). When soils are disturbed, this carbon is released as CO₂ and CH₄, accelerating climate change. Understanding soil functions is therefore not only an agricultural issue — it sits at the intersection of biodiversity conservation, climate regulation, water security, and food sovereignty.
🌍 Why This Matters Soil underpins virtually every terrestrial ecosystem service: it filters water, cycles nutrients, supports plant growth, regulates atmospheric carbon, and harbours a vast proportion of Earth's biodiversity. The degradation of soil is simultaneously a biodiversity crisis, a climate crisis, and a food security crisis — making it one of the most consequential and underappreciated environmental challenges of the 21st century.
Core Concepts & Definitions
Before we can understand how soil functions within ecosystems, we need to appreciate what soil actually is. Most people think of soil as simply "dirt" — an inert substrate. But soil is a living system, a dynamic interface between the lithosphere, biosphere, hydrosphere, and atmosphere. Its properties emerge from the interaction of five