Chapter 8: Earth Systems and Resources

Summary

This chapter examines the physical foundations of ecology: how plate tectonics shapes habitats, how soils form and erode, how the atmosphere drives weather patterns, and how solar radiation creates climate zones. Students learn about watersheds, the Coriolis effect, and albedo. After completing this chapter, students will be able to explain how Earth's physical systems create the conditions that support life.

Concepts Covered

This chapter covers the following 22 concepts from the learning graph:

Plate Tectonics
Convergent Boundaries
Divergent Boundaries
Transform Boundaries
Soil Formation
Soil Erosion
Soil Horizons
Soil Texture Triangle
Soil Composition
Earth's Atmosphere
Atmospheric Layers
Troposphere
Stratosphere
Global Wind Patterns
Coriolis Effect
Convection Cells
Watersheds
Solar Radiation
Seasons
Climate Patterns
Rain Shadow Effect
Albedo

Prerequisites

This chapter builds on concepts from:

Bailey Says: Welcome, Builders!

Today we're going big -- like, PLANET big! Before we can understand where life lives and why, we need to understand the physical stage it performs on. From drifting continents to spinning winds to the dirt under your feet, Earth's physical systems set the rules for every ecosystem on the planet. Everything's connected -- and it starts with rock, air, water, and sunlight!

The Restless Earth: Plate Tectonics

The ground beneath your feet feels solid, but it's actually moving. Right now. About as fast as your fingernails grow -- roughly 2-10 centimeters per year.

Plate tectonics is the theory that Earth's outer shell (the lithosphere) is broken into massive slabs called tectonic plates that float on the semi-molten asthenosphere below. These plates carry continents and ocean floors, and where they interact, dramatic things happen -- mountains rise, oceans open, volcanoes erupt, and earthquakes shake the ground.

Why should ecologists care about plate tectonics? Because plate movements:

Create and destroy habitats over geological time
Build mountain ranges that alter climate and create biodiversity hotspots
Separate and reconnect continents, driving speciation and extinction
Generate volcanic soils that support incredibly productive ecosystems
Shape ocean currents that distribute heat around the planet

Boundary Types

Plates interact at three types of boundaries:

Convergent boundaries occur where plates collide. When an oceanic plate meets a continental plate, the denser oceanic plate dives beneath (subduction), creating deep ocean trenches and volcanic mountain chains like the Andes. When two continental plates collide, neither subducts easily -- instead, the crust crumples upward into massive mountain ranges like the Himalayas. These mountains create rain shadows, alter wind patterns, and generate enormous biodiversity by creating diverse habitats at different elevations.

Divergent boundaries occur where plates pull apart. Magma wells up to fill the gap, creating new crust. The Mid-Atlantic Ridge is a divergent boundary running down the center of the Atlantic Ocean, slowly pushing Europe and North America farther apart. On land, divergent boundaries create rift valleys like the East African Rift -- which, not coincidentally, is where some of humanity's oldest fossil ancestors were found.

Transform boundaries occur where plates slide past each other horizontally. The San Andreas Fault in California is the most famous example. Transform boundaries generate earthquakes but don't typically create or destroy crust. However, the disturbance they cause can reshape landscapes and reset ecological succession.

Boundary Type	Plate Motion	Features Created	Ecological Significance
Convergent	Plates collide	Mountains, trenches, volcanoes	Elevation gradients, rain shadows, fertile volcanic soil
Divergent	Plates separate	Rift valleys, mid-ocean ridges	New habitats, isolation drives speciation
Transform	Plates slide past	Fault lines, earthquakes	Disturbance resets succession, reshapes landscapes

The Ground Beneath Us: Soils

If plate tectonics is ecology's stage builder, soil is the stage itself. Nearly every terrestrial food web starts with plants, and plants start with soil.

Soil Formation

Soil formation (pedogenesis) is agonizingly slow -- it takes roughly 500 to 1,000 years to form just 2.5 centimeters (one inch) of topsoil. Five factors drive soil formation, easily remembered by the acronym CLORPT:

Climate: temperature and precipitation control weathering rates
Organisms: plants, animals, fungi, and bacteria break down rock and add organic matter
Relief (topography): slope angle and aspect affect drainage, erosion, and sun exposure
Parent material: the underlying rock determines mineral composition
Time: soil development takes centuries to millennia

Soil Composition

Soil composition is a mix of four components:

Minerals (~45%): sand, silt, and clay particles from weathered rock
Organic matter (~5%): decomposed plant and animal material (humus)
Water (~25%): held in pore spaces between particles
Air (~25%): fills remaining pore spaces, providing oxygen to roots and organisms

That 5% organic matter punches way above its weight -- it's responsible for most of soil's nutrient-holding capacity, water retention, and structural integrity.

Bailey Says: Think About It!

Dam, think about this: a single teaspoon of healthy soil contains more microorganisms than there are people on Earth -- up to 1 billion bacteria, several yards of fungal threads, and thousands of protozoa. Soil isn't dirt. It's one of the most complex ecosystems on the planet. Everything's connected, right down to the ground beneath your feet!

Soil Horizons

Dig a hole deep enough and you'll see distinct layers called soil horizons. A vertical cross-section showing all horizons is called a soil profile:

O horizon (organic): Surface layer of decomposing leaves, twigs, and organisms. Dark and rich.
A horizon (topsoil): Mineral soil mixed with humus. Where most roots grow and most biological activity occurs. The layer most critical for agriculture.
B horizon (subsoil): Accumulation zone where minerals leached from above collect. Often clay-rich and dense.
C horizon (parent material): Partially weathered rock fragments. Little biological activity.
R horizon (bedrock): Unweathered solid rock. The foundation from which soil ultimately derives.

The Soil Texture Triangle

The relative proportions of sand, silt, and clay particles determine soil texture, which profoundly affects drainage, nutrient retention, and plant growth. The soil texture triangle is the tool ecologists and farmers use to classify soil.

Sand (0.05-2 mm): Large particles, excellent drainage, poor nutrient retention
Silt (0.002-0.05 mm): Medium particles, moderate drainage and nutrient retention
Clay (<0.002 mm): Tiny particles, poor drainage, excellent nutrient retention

The ideal soil for most plants is loam -- a balanced mix of roughly 40% sand, 40% silt, and 20% clay. Loam combines good drainage with good nutrient and water retention.

Diagram: Soil Horizons and Texture Explorer

Soil Horizons and Texture Explorer

Type: microsim sim-id: soil-explorer
Library: p5.js
Status: Specified

Bloom Level: Apply Bloom Verb: Classify Learning Objective: Students will classify soil types using the texture triangle and identify soil horizons in a profile diagram. Instructional Rationale: Split-screen interactive combines two related but distinct concepts (horizons and texture) in one tool, reinforcing that soil structure and composition work together.

Visual: Left panel: Cross-section soil profile showing O, A, B, C, and R horizons with realistic colors and textures. Hovering over each horizon highlights it and displays description, typical depth, composition, and ecological role. Animated earthworms, roots, and fungi at appropriate depths. Right panel: Interactive soil texture triangle. Three sliders (sand %, silt %, clay %) constrained to sum to 100%. As student adjusts sliders, a dot moves on the triangle showing the current soil classification. The classification name (sandy loam, silty clay, etc.) updates in real-time. Below, a brief description of that soil type's drainage, nutrient retention, and best agricultural uses. Color the triangle regions in earth tones corresponding to soil color.

Soil Erosion

Soil erosion -- the removal of topsoil by wind, water, or human activity -- is one of the most serious environmental problems on Earth. We lose soil 10 to 100 times faster than nature creates it.

Causes of accelerated erosion include:

Deforestation (removing root systems that hold soil in place)
Overgrazing (stripping vegetation that protects the surface)
Poor agricultural practices (tilling bare soil, farming on steep slopes)
Construction and development (exposing bare earth)

Prevention strategies include:

Contour plowing (plowing along the contour of slopes, not up and down)
Terracing (creating flat "steps" on hillsides)
Cover cropping (planting vegetation specifically to hold soil)
No-till farming (planting without disturbing the soil surface)
Riparian buffers (maintaining vegetation along waterways)

Watersheds: Where Water Flows

A watershed (also called a drainage basin or catchment) is the entire area of land that drains into a particular body of water -- a stream, river, lake, or ocean. Watersheds are defined by topography: the ridgelines and high points that separate one drainage area from another.

Every point on land belongs to a watershed. When rain falls on your school's roof, it flows downhill through gutters, streets, storm drains, and streams -- eventually reaching a river and then the ocean. Everything upstream affects everything downstream, which is why watershed management matters enormously for water quality, flood control, and ecosystem health.

Watersheds nest inside each other like Russian dolls. Your local creek drains into a river, which drains into a larger river, which drains into the ocean. The Mississippi River watershed covers roughly 40% of the contiguous United States -- meaning actions taken by a farmer in Montana can affect water quality in the Gulf of Mexico.

Bailey Says: Here's a Tip!

Want to find your own watershed? The EPA has an interactive tool at epa.gov/waterdata that lets you click anywhere on a map and see which watershed you're in. Try it -- you might be surprised at where your water goes! Let's build on that!

Earth's Atmosphere: The Ocean of Air

We live at the bottom of an ocean of gas. Earth's atmosphere is a thin shell of air extending roughly 480 km above the surface, though 99% of its mass is concentrated in the lowest 30 km.

The atmosphere's composition:

Nitrogen (N₂): ~78%
Oxygen (O₂): ~21%
Argon (Ar): ~0.93%
Carbon dioxide (CO₂): ~0.04% (and rising)
Trace gases and water vapor: variable

Atmospheric Layers

The atmosphere is divided into atmospheric layers based on temperature changes with altitude:

Troposphere (0-12 km): Where we live. Where weather happens. Temperature decreases with altitude (about 6.5°C per km). The troposphere contains about 75% of the atmosphere's mass and virtually all its water vapor. This is where all weather phenomena occur -- clouds, rain, snow, thunderstorms, and hurricanes.

Stratosphere (12-50 km): Temperature increases with altitude because the ozone layer (O₃) absorbs UV radiation, warming this layer. The stratosphere is calm, dry, and stable -- perfect for jet aircraft, terrible for weather. The ozone layer here is critical for life: it blocks most of the sun's harmful ultraviolet radiation.

Above the stratosphere are the mesosphere (50-80 km) and thermosphere (80-700 km), but these have less direct ecological significance.

Solar Radiation, Seasons, and Climate

Everything on Earth -- every wind, every wave, every living thing -- runs on energy from the sun. Understanding how solar radiation is distributed across the planet is the key to understanding climate, weather, and biomes.

Uneven Heating

The Earth is a sphere, which means solar radiation hits different latitudes at different angles:

At the equator, sunlight strikes nearly perpendicular to the surface, concentrating energy into a small area
At the poles, sunlight strikes at a low angle, spreading the same energy over a much larger area
The result: the tropics receive about 2.4 times more solar energy per square meter than the poles

This uneven heating is the engine that drives global atmospheric and oceanic circulation.

Seasons

Seasons exist not because Earth's distance from the sun changes (we're actually closest in January!), but because Earth's axis is tilted 23.5° relative to its orbital plane. This axial tilt means:

Summer: Your hemisphere tilts toward the sun, receiving more direct sunlight for longer days
Winter: Your hemisphere tilts away from the sun, receiving less direct sunlight for shorter days
Equinoxes: Neither hemisphere tilts toward the sun; day and night are approximately equal

Seasons drive phenology -- the timing of biological events like flowering, migration, hibernation, and breeding. As climate change shifts seasonal patterns, organisms must adapt, move, or face decline.

Albedo: The Reflectivity Factor

Albedo is the fraction of incoming solar radiation that a surface reflects. It ranges from 0 (absorbs everything) to 1 (reflects everything):

Fresh snow: 0.80-0.90 (reflects most sunlight)
Ocean water: 0.06-0.10 (absorbs most sunlight)
Forest: 0.10-0.20
Desert sand: 0.30-0.40
Clouds: 0.40-0.80

Albedo creates powerful feedback loops. As Arctic ice melts, dark ocean water replaces reflective ice, absorbing more heat, which melts more ice -- a positive feedback loop accelerating warming. This is one of the reasons the Arctic is warming roughly four times faster than the global average.

Diagram: Solar Radiation and Albedo Simulator

Solar Radiation and Albedo Simulator

Type: microsim sim-id: solar-albedo
Library: p5.js
Status: Specified

Bloom Level: Apply Bloom Verb: Calculate Learning Objective: Students will calculate the net energy absorbed by different surfaces and predict how albedo changes affect local temperature. Instructional Rationale: Manipulating surface types and seeing real-time energy budgets makes the abstract concept of albedo tangible and connects it to climate feedback loops.

Visual: Side view of Earth's surface with incoming solar arrows from above. A dropdown or row of clickable surface types (snow, ocean, forest, desert, city, ice) changes the ground surface. Reflected arrows bounce off the surface proportional to albedo -- more arrows reflected for high-albedo surfaces. A temperature gauge on the right shows surface temperature rising or falling based on net absorbed energy. Below, a numerical display shows: incoming radiation, reflected radiation, absorbed radiation, and albedo value. A "Climate Feedback" toggle shows how changing from ice to ocean creates a positive feedback loop, with an animated cycle diagram. Color: incoming arrows yellow, reflected arrows white, absorbed shown as red glow on surface.

Global Wind Patterns and the Coriolis Effect

The uneven heating of Earth's surface creates massive air circulation patterns that distribute heat, moisture, and even organisms around the globe.

Convection Cells

Warm air rises, cool air sinks -- this basic principle, scaled up to planetary size, creates three convection cells in each hemisphere:

Hadley Cell (0°-30° latitude): Hot equatorial air rises, flows poleward at high altitude, cools and sinks at about 30°. This creates tropical rainforests at the equator (where warm, moist air rises and dumps rain) and deserts at 30° (where cool, dry air descends). Not a coincidence that the Sahara, Arabian, and Sonoran deserts all sit near 30° latitude.
Ferrel Cell (30°-60° latitude): An indirect, thermally-driven cell. Surface winds blow poleward, creating the prevailing westerlies that dominate weather in the midlatitudes (including most of the US and Europe).
Polar Cell (60°-90° latitude): Cold air sinks at the poles and flows equatorward along the surface. Where polar air meets midlatitude air (around 60°), it creates the polar front -- a zone of stormy weather.

The Coriolis Effect

If Earth didn't rotate, winds would blow in straight lines from high to low pressure. But Earth does rotate, and this creates the Coriolis effect -- an apparent deflection of moving air (and water) caused by Earth's rotation.

In the Northern Hemisphere, moving objects deflect to the right
In the Southern Hemisphere, moving objects deflect to the left

The Coriolis effect is what turns simple north-south winds into the curved global wind patterns we observe:

Trade winds (0°-30°): Blow from east to west (northeast in NH, southeast in SH). These reliable winds powered centuries of sailing commerce.
Westerlies (30°-60°): Blow from west to east. This is why weather systems in the US generally move from west to east.
Polar easterlies (60°-90°): Blow from east to west near the poles.

Bailey Says: Think About It!

Wood you believe that global wind patterns explain why California has rainforests in the north and deserts in the south? The westerlies bring moist Pacific air to the Pacific Northwest, while the descending air of the Hadley cell creates the dry conditions of Southern California and the Sonoran Desert. Geography plus atmospheric physics equals biomes. See how it all fits together?

Diagram: Global Wind and Convection Cell Model

Global Wind and Convection Cell Model

Type: microsim sim-id: global-winds
Library: p5.js
Status: Specified

Bloom Level: Understand Bloom Verb: Describe Learning Objective: Students will describe how convection cells, the Coriolis effect, and global wind patterns interact to create Earth's major climate zones. Instructional Rationale: A cross-section view of Earth's atmosphere with animated wind arrows and convection loops makes invisible atmospheric processes visible and shows students how physics creates the biome map.

Visual: Cross-section of Earth from pole to pole (semicircle) with the atmosphere shown as concentric layers above. Three convection cells in each hemisphere shown as animated circulation loops with arrows. Surface wind directions shown with blue arrows labeled (Trade Winds, Westerlies, Polar Easterlies). Coriolis deflection shown with curved arrow overlays. At the surface, icons show resulting biomes: rainforest at equator, desert at 30°, temperate forest at 45°, tundra near poles. A toggle switches between "No Rotation" (straight winds) and "With Rotation" (Coriolis-deflected winds) to show the effect. Precipitation indicators (rain droplets) at rising air zones (equator, 60°) and dry indicators (sun icons) at sinking air zones (30°, 90°). Interactive: hover over any latitude band to see wind name, direction, typical weather, and associated biome.

Climate Patterns and the Rain Shadow Effect

Climate patterns -- the long-term averages of temperature, precipitation, and wind for a region -- emerge from the interaction of all the physical systems we've discussed: solar angle, axial tilt, atmospheric circulation, ocean currents, topography, and albedo.

Two key factors shape regional climate:

Latitude: Controls solar angle and day length, primarily determining temperature
Topography: Mountains interact with wind patterns to create dramatic local climate variation

The rain shadow effect is one of the most dramatic examples of how topography shapes climate. When moist air is pushed up over a mountain range by prevailing winds:

Windward side (facing the wind): Air rises, cools, and water vapor condenses into clouds and precipitation. This side is typically lush and wet.
Mountain summit: Maximum precipitation, often as snow.
Leeward side (opposite the wind): Air descends, warms, and dries out. This side is arid -- the "rain shadow."

The Pacific Northwest rainforests (windward) and the dry Eastern Washington/Oregon steppe (leeward) of the Cascade Range are a textbook example. The Himalayas create the Gobi Desert on their leeward side. The Andes create the Atacama Desert, the driest place on Earth.

Diagram: Rain Shadow Effect Visualizer

Rain Shadow Effect Visualizer

Type: microsim sim-id: rain-shadow
Library: p5.js
Status: Specified

Bloom Level: Analyze Bloom Verb: Explain Learning Objective: Students will explain how mountain ranges create wet and dry climate zones through the rain shadow effect. Instructional Rationale: Animated air flow over a mountain cross-section with real-time humidity and temperature gauges makes the invisible processes of adiabatic cooling and warming visible and intuitive.

Visual: Side-view cross-section showing ocean on the left, a mountain in the center, and lowlands on the right. Animated air parcels (blue dots/clouds) flow from left to right. As air rises over the windward slope, parcels cool (temperature gauge drops), humidity rises, clouds form, and rain falls (animated droplets). At the summit, heavy precipitation shown. On the leeward side, air descends, warms (temperature gauge rises), humidity drops, and the landscape becomes brown and arid. A slider controls mountain height (500m to 5000m), and as the mountain gets taller, the rain shadow effect becomes more extreme. Vegetation changes with moisture: lush forest on windward side, sparse scrubland on leeward side. Labels show temperature and relative humidity at each stage. A "Real Examples" dropdown overlays data from actual mountain ranges (Cascades, Himalayas, Andes, Sierra Nevada).

Media Literacy Moment: Soil and Land Use Claims

"We only have 60 harvests left!" This alarming claim about soil loss has circulated widely since a UN official mentioned it in 2014. But is it accurate?

Source-checking exercise:

Origin: The claim traces to a 2014 speech by a UN Food and Agriculture Organization (FAO) official, not a peer-reviewed study.
Evidence: The FAO itself later clarified that the figure was a rough average, not a rigorous global estimate. Soil degradation rates vary enormously by region and farming practice.
Nuance: Some soils ARE severely degraded and may be unproductive within decades. Others are well-managed and improving. A single global number obscures critical local variation.
Better framing: The scientific consensus is that soil erosion IS a serious problem -- we lose agricultural soil faster than it forms in many regions -- but the "60 harvests" figure oversimplifies a complex, regionally variable issue.

The takeaway: be especially cautious with single numbers that claim to summarize a complex global problem. Good science embraces complexity and uncertainty.

Bailey Says: Watch Out!

Common mistake alert! Don't confuse weather with climate. Weather is what's happening outside RIGHT NOW -- today's temperature, whether it's raining. Climate is the long-term average pattern over 30+ years. A single cold day doesn't disprove global warming, just like a single hot day doesn't prove it. Climate is what you expect; weather is what you get.

Connections: How Earth Systems Shape Ecology

Every concept in this chapter connects to create the physical template that life adapts to:

Plate tectonics builds mountains that create rain shadow effects and diverse elevation-based habitats
Soil formation depends on climate patterns (temperature and precipitation drive weathering) and parent material from tectonic processes
Solar radiation combined with Earth's tilt creates seasons that drive biological rhythms
Convection cells powered by uneven solar heating create global wind patterns that distribute moisture, determining where deserts and rainforests form
The Coriolis effect curves these winds, creating the trade winds and westerlies that shape climate patterns
Albedo creates feedback loops that amplify or dampen temperature changes
Watersheds connect upland soils to downstream aquatic ecosystems, linking soil erosion to water quality
Soil horizons, texture, and composition determine which plants can grow where, forming the foundation of terrestrial food webs

Understanding these physical systems is essential for understanding everything that comes next in this course -- from pollution to climate change to conservation.

Key Terms Summary

Term	Definition
Plate Tectonics	Theory that Earth's lithosphere is divided into moving plates
Convergent Boundaries	Where tectonic plates collide
Divergent Boundaries	Where tectonic plates pull apart
Transform Boundaries	Where tectonic plates slide horizontally past each other
Soil Formation	The slow process of soil development from parent material
Soil Erosion	Removal of topsoil by wind, water, or human activity
Soil Horizons	Distinct layers visible in a vertical soil cross-section
Soil Texture Triangle	Tool for classifying soil by proportions of sand, silt, and clay
Soil Composition	The mixture of minerals, organic matter, water, and air in soil
Earth's Atmosphere	The thin shell of gases surrounding Earth
Atmospheric Layers	Temperature-defined divisions of the atmosphere
Troposphere	Lowest atmospheric layer where weather occurs (0-12 km)
Stratosphere	Second atmospheric layer containing the ozone layer (12-50 km)
Global Wind Patterns	Planetary-scale wind systems driven by uneven heating and rotation
Coriolis Effect	Apparent deflection of moving air/water due to Earth's rotation
Convection Cells	Large-scale atmospheric circulation loops driven by heating differences
Watersheds	Land area that drains into a particular body of water
Solar Radiation	Energy from the sun that drives Earth's climate and life
Seasons	Cyclical climate variations caused by Earth's axial tilt
Climate Patterns	Long-term averages of temperature, precipitation, and wind
Rain Shadow Effect	Dry conditions on the leeward side of a mountain range
Albedo	Fraction of incoming solar radiation reflected by a surface

Self-Test Questions

Why do most of the world's major deserts occur near 30° latitude?

At approximately 30° latitude, air from the Hadley Cell descends after losing its moisture at the equator. This descending air is dry and warm, suppressing cloud formation and precipitation. The result is arid conditions -- which is why the Sahara, Arabian, Sonoran, and Australian deserts all cluster near 30° N or S latitude. The pattern is driven by convection cells and the uneven distribution of solar radiation.

Explain why the windward side of a mountain is wet and the leeward side is dry.

The rain shadow effect: Prevailing winds push moist air toward a mountain. As air rises along the windward slope, it cools adiabatically. Cooler air holds less moisture, so water vapor condenses into clouds and falls as precipitation. By the time the air passes over the summit and descends the leeward slope, it has lost most of its moisture. The descending air also warms as it compresses, further reducing relative humidity. The result: lush vegetation on the windward side, arid conditions on the leeward side.

A soil sample is 60% sand, 20% silt, and 20% clay. Using the soil texture triangle, what would this soil be classified as, and what are its properties?

This soil would be classified as sandy clay loam. It would have relatively good drainage due to the high sand content, moderate nutrient retention from the clay fraction, and fair water-holding capacity. It would drain faster than a clay soil but hold more nutrients than pure sand. For agriculture, it would be decent for drought-tolerant crops but might need organic matter amendments to improve water retention.

How does albedo create a positive feedback loop in the Arctic?

Arctic ice has high albedo (0.80-0.90), reflecting most sunlight back to space. As global temperatures rise, ice melts, exposing dark ocean water with low albedo (0.06-0.10). Dark water absorbs more solar energy, warming further, which melts more ice, exposing more dark water -- a self-amplifying positive feedback loop. This is why the Arctic is warming approximately four times faster than the global average.

What are the five factors of soil formation, and how does each influence the type of soil that develops?

The five factors (CLORPT): Climate -- temperature and precipitation control chemical weathering rates and organic matter decomposition. Organisms -- plants add organic matter, burrowing animals mix soil layers, bacteria and fungi decompose material. Relief (topography) -- steep slopes lose soil to erosion, flat areas accumulate deep soils, south-facing slopes (in NH) are warmer and drier. Parent material -- the type of bedrock determines mineral content (granite produces sandy soils, basalt produces clay-rich soils). Time -- young soils are thin and poorly developed; ancient soils have well-defined horizons and deep profiles.

Bailey Says: Outstanding Work, Builders!

You just mastered the physical foundations of ecology -- from the tectonic forces that build continents to the wind patterns that distribute rain to the soil that feeds every food web on land. Dam, that's a lot of ground to cover (pun absolutely intended)! You now understand why deserts sit where they do, why mountains create biodiversity hotspots, and why soil is way more than just dirt. Everything's connected -- and now you can trace those connections from the center of the Earth to the top of the atmosphere!

See Annotated References