4. Crash Course Geography: Physical Geography and Earth's Four Spheres
Fieldwork, Photography, and the Record of Change
When fieldwork is done, taking photos serves not only to capture memories but to create an important record of moments in history. A vivid example is a trip to Madagascar where hundreds of photos of erosional formations on rolling hillsides reveal how the island’s highlands have shifted from a broadly forested landscape to one where deforestation has produced serious gashes and erosional gullies called lavaca. With fewer trees, soils become more vulnerable to landslide‑like events, setting the stage for further dramatic landscape changes. This illustrates how images from the field become evidence of environmental change over time and help us understand processes at work in the real world.
The landscape is not permanent. It has changed as continents shifted and humans interacted with the environment, and it will continue to change. Because the planet is a super dynamic place, some changes occur slowly—watching continents drift or mountain ranges like the Rocky Mountains grow would require millions of years. In contrast, a storm or an avalanche can alter the landscape in the blink of an eye. Both slow and rapid changes profoundly influence our lives, from daily decisions like what we wear to where we choose to live. All of these changes, both above and below the Earth’s surface, fall under the umbrella of physical geography, and Crash Course Geography uses physical geography as the lens for telling the stories of the Earth.
Physical Geography, Human Geography, and the Geo‑Ecosphere
Until now we’ve discussed tools and ideas common to geography, but the Earth is large and complex. Traditionally, geography is studied through two interconnected parts: physical geography and human geography. Physical geography focuses on recognizing environmental characteristics and the processes that create, modify, and destroy environments, while human–environment interactions are fundamental to studying geography. As physical geographers, we seek answers in processes that happen without humans and because of humans.
We explore a specific space—the geo‑ecosphere—the narrow zone on Earth’s surface that contains all the landscapes and major systems interacting to create our dynamic planet. By breaking the Earth into distinct systems, we can look for connections that help us understand complex problems such as climate change or the loss of biodiversity. In physical geography, four major Earth systems are identified: the atmosphere, the hydrosphere, the lithosphere, and the biosphere. The atmosphere comprises the layers of air surrounding Earth that give us clouds, weather, the ozone layer, and the air we breathe. The hydrosphere includes all water on, under, and above the planet’s surface—water in soils, groundwater, oceans, lakes, ice caps, streams, and even water within organisms and in the atmosphere. The lithosphere is the rocky outermost layer of Earth, forming continents and the ocean floor, while the biosphere encompasses all regions where life exists. No matter which focus we choose within physical geography, all four spheres play a role.
Ecosystems are communities of living things interacting with their nonliving environment based on these underlying Earth systems. Consider the Thought Bubble about the Great Barrier Reef: off the Northeastern coast of Australia, the reef is the world’s largest coral reef system, consisting of almost 3{,}000 individual reefs and hosting more than 9{,}000 different species. These organisms work together to build the reef’s structure; the skeleton of the reef is formed by hard corals that secrete calcium carbonate, which hardens into limestone. This limestone is part of the lithosphere and creates the rock foundation that protects corals and other organisms from waves. Even after corals die, their limestone remains and provides a basis for new corals to grow and thrive. The Great Barrier Reef exists underwater in the Pacific Ocean, so it is surrounded by the hydrosphere, and the atmosphere continues to interact with this marine ecosystem through weather systems. Delicate coral ecosystems rely on interactions among all four spheres. The reef’s thriving conditions often occur where clashes between the hydrosphere and atmosphere generate waves; thousands of cubic kilometers of ocean water flow through the reef each year, bringing food and oxygen and helping moderate temperatures. However, intense winds and towering waves from Pacific cyclones can destroy softer corals and damage hard corals, though cyclones may also bring cooler water and help clean sediment from the reef. These interactions illustrate how the Earth’s systems work together and occasionally come into conflict. Looking for interactions among all four spheres helps identify what supports ecosystems and where changes might threaten them. We can also anticipate how the Earth formed these spheres and how it moves by examining their interactions.
The Sun, Insulation, and the Driver of the Earth’s Systems
The Sun and insulation are the drivers and influencers of the four Earth systems. For example, the Sun’s energy heats liquid water, causing evaporation of water into vapor. Water vapor can condense in the atmosphere, forming clouds and rain. This rain may feed rivers, lakes, or become part of glacial processes as water freezes into ice. Over time, glaciers may move down mountainsides, altering surfaces and creating habitats for microscopic life. As physical geographers, our area of study includes everything that the light touches and more, illustrating the vast scope of the field. Because the Earth’s spheres are so expansive, physical geographers specialize in different realms and processes. The narrative even gestures toward a Guatemala banana example as a way to imagine a field study—though the lecture pivots to Iceland to illustrate specialization. The Iceland example helps ground the discussion in concrete processes and regional specifics.
Iceland: Geology, Landforms, and the Geomorphological Perspective
Iceland’s land was originally settled by Nordic people around August, though the region appears in historical records under other names such as Snæland or Gardar’s Isle in sagas, reflecting a long-standing human presence. Iceland sits on the northern part of the Mid‑Atlantic Ridge, an underwater mountain range that runs north–south through the Atlantic Ocean. The island’s topography results from processes both above and below the surface, including occasional lava eruptions that contribute to ongoing growth. As geomorphologists, physical geographers study the origin and evolution of Earth’s surface shapes, investigating weathering, glaciation, and other processes that sculpt landscapes. The soils in Iceland are largely volcanic in origin, called andesols, which are rich in nutrients due to volcanic ash. In the past, these soils supported forests and grasslands, but about a thousand years ago, settlers cleared much of the forests. This led to overgrazing by cattle and sheep, exposing the nutrient-rich topsoil to erosion and reducing soil quality for plants. Here the field of pedology—the study of soil types and how soils form—interacts with practical conservation efforts, aided by a group referred to in the transcript as podologists (note the transcript’s phrasing uses podologists where pedology is the standard term).
Iceland’s unique combination of glaciers and volcanoes shapes both the land and the water. Hydrology—the study of how water moves, is managed, and is distributed above and below the surface—becomes especially important in Iceland as glaciers melt and runoff increases, affecting river flow and sediment transport. By 2020, about 10\% of Iceland was covered by glaciers. At the same time, magma near the surface provides heat for geysers and hot springs, increasing river discharge and runoff. Hydrologists in Iceland might map sediment sources in rivers or assess which parts of a city are most at risk of flooding, while also helping manage water resources to generate hydropower. By 2015, almost 100\% of Icelandic electricity came from renewable sources, with about 73\% coming from hydropower, reflecting how physical geography informs energy policy and everyday life. The integration of geology, hydrology, and energy planning shows how physical geography integrates with real-world life.
Iceland’s climate is also shaped by its island geography in the North Atlantic Ocean, where ocean–atmosphere interactions shape weather and climate. Climatology—the study of atmospheric conditions over time—interacts with oceanography—the study of oceans’ past, present, and future features. The North Atlantic Drift Current warms the region, helping moderate Iceland’s climate by delivering warmer water to the north and resulting in damp, cool summers and relatively mild winters for its latitude. However, winters are not uniformly mild; atmospheric energy fluctuations can bring severe storms, such as a December 2019 blizzard that dumped up to 3\,\text{m} (approximately 9\,\text{ft}) of snow. Even with occasional extreme weather, Iceland sustains a thriving biosphere: biogeography studies the distribution of plants and animals, such as puffins, skuas, and kittywakes along sea cliffs, and Arctic foxes, reindeer, and rabbits inland. Polar bears may occasionally pass by on icebergs drifting from Greenland. Vegetation is limited by factors like overgrazing, deforestation, glacial movement, and volcanic activity; grasses and low shrubs such as heather dominate, with few large trees. As biogeographers, we might explore how vegetation along stream banks affects flooding, or we might contribute to conservation planning and protected areas. A geographer’s focus, in contrast to an ecologist, is on how ecological processes distribute across space and how species move and change over time. In short, physical geography emphasizes spatial patterns and the interactions among the four spheres.
The Earth’s story stretches back more than 4.5\times 10^{9} years, and we will explore more in the next session. Describing these dynamic twists and turns helps us understand our role on this planet and our future.
Indigenous Lands Acknowledgement and the Real-World Context of Geography
Many maps and borders reflect modern geopolitical divisions decided without consultation with or recognition of the land’s original inhabitants. Place names often do not reflect Indigenous or Aboriginal languages. Crash Course Geography acknowledges these relationships and encourages learning about the history of the land you call home through resources such as nativelands.ca and by engaging with local Indigenous and Aboriginal nations and their resources.
Community, Resources, and the Path Forward
Thank you for watching Crash Course Geography, a program produced with the help of a community of viewers and contributors. If you’d like to help keep Crash Course free for everyone, you can join the Patreon community and support ongoing production.
Quick Recap of Key Concepts and Connections
- Physical geography focuses on four Earth systems—the atmosphere, hydrosphere, lithosphere, and biosphere—and how they interact, both with each other and with humans. The geo‑ecosphere is the integrated space where these interactions occur, and understanding it helps address big problems like climate change and biodiversity loss.
- The Sun and insulation drive all Earth systems via energy input, the water cycle, weather, and climate, which in turn shape landscapes, habitats, and human decisions.
- Case studies like the Great Barrier Reef illustrate how four spheres interact: corals build limestone (lithosphere) and live within the hydrosphere, while atmospheric conditions create waves and weather that shape reef health.
- Iceland serves as a rich natural laboratory to see geomorphology in action: volcanic soils (andesols), active tectonics (Mid‑Atlantic Ridge), glaciation, hydrology and hydropower, and climate moderated by ocean currents. Human activities such as deforestation and grazing have altered soil and landscape dynamics, highlighting the need for pedology and podology in soil conservation.
- The role of biogeography and ecologists vs. geographers helps explain how life is distributed across landscapes and how human and ecological processes are spatially organized and evolve over time.
- Ethical considerations include acknowledging Indigenous lands and histories in mapmaking and geography, and encouraging engagement with Indigenous knowledge through reliable resources.
- Quantitative notes from the episode include: the Great Barrier Reef houses ~3{,}000 reefs and >9{,}000 species; the reef experiences flows of thousands of cubic kilometers of ocean water annually; Iceland’s glaciers cover ~10\% of the country; Iceland’s electricity is nearly 100\% renewable, with ~73\% from hydropower; climate variability can yield extreme events like a 3\,\text{m} snow event (~9\,\text{ft}) in one storm; Earth’s age is about 4.5\times 10^{9} years.