Earth’s terrain spans everything from ocean trenches nearly 11 kilometers deep to mountain peaks almost 9 kilometers high, creating a total relief of roughly 20 kilometers across the planet’s surface. About 71% of that surface sits beneath ocean water, meaning the majority of Earth’s terrain is actually underwater. The remaining 29% is land, split among forests, deserts, grasslands, ice sheets, and a growing footprint of human-modified ground.
Land Versus Ocean
The single most defining feature of Earth’s terrain is how much of it you’ll never see without a submarine. Over 96% of all surface water is saline ocean water, and together the oceans cover roughly 361 million square kilometers. Land accounts for about 149 million square kilometers, or less than a third of the total. This ratio has stayed relatively stable over human history, though coastlines shift as sea levels rise and fall.
The average depth of the ocean floor is about 3.5 kilometers (2.2 miles) below the surface. Average land elevation, by contrast, sits at roughly 840 meters (about half a mile) above sea level. So the planet’s terrain is, on average, far deeper below the waterline than it is tall above it.
What the Ocean Floor Looks Like
If you could drain the oceans, you’d find terrain just as dramatic as anything on land. Starting from any coastline, you’d first cross the continental shelf, a relatively shallow zone usually less than a few hundred feet deep. In some places it barely exists; in others it stretches for hundreds of miles. These shallow waters tend to be biologically rich because sunlight still reaches much of the bottom and nutrients flow in from the land.
Beyond the shelf, the seafloor drops steeply down the continental slope and flattens into abyssal plains. These vast expanses sit at depths of over 10,000 feet and cover about 70% of the ocean floor, making them the single largest habitat on Earth. Despite the name “plains,” they’re broken up by hills, valleys, and seamounts (underwater mountains that can rise thousands of meters from the surrounding floor).
Winding through the ocean basins is the mid-ocean ridge, an underwater volcanic mountain range stretching over 40,000 miles. That makes it the longest mountain range on the planet, dwarfing anything on land. It rises to an average depth of about 8,200 feet below the surface, where new crust is constantly being created as molten rock pushes up from below.
Major Land Terrain Types
Earth’s land surface breaks down into three broad categories: tree-covered areas, short vegetation (grasslands, shrublands, tundra, and cropland), and bare ground (deserts, rock, ice, and sand). As of 1982 baseline measurements, roughly 31.6 million square kilometers had tree canopy cover, about 64.5 million square kilometers had short vegetation, and about 37.4 million square kilometers were bare ground. Those proportions have shifted over the decades. Global tree cover has actually increased by about 2.24 million square kilometers (a 7.1% gain relative to 1982), largely from forest regrowth and tree plantations in Asia and Europe. Bare ground has decreased by about 1.16 million square kilometers, or 3.1%, mostly because agricultural expansion in Asia converted barren land to cropland.
Forests cluster most densely in the tropics (the Amazon basin, the Congo basin, Southeast Asia) and in the boreal belt across Canada, Scandinavia, and Siberia. Deserts dominate North Africa, the Arabian Peninsula, Central Asia, and interior Australia. Grasslands and savannas sweep across sub-Saharan Africa, the North American Great Plains, the South American Pampas, and the Central Asian steppe.
Ice Sheets and Glaciers
Permanent ice is a terrain type in its own right. The ice sheets atop Greenland and Antarctica store about two-thirds of all the fresh water on Earth and cover a combined area of roughly 14 million square kilometers. Antarctica alone holds ice up to 4.8 kilometers thick in places. These ice sheets are losing mass: Antarctica sheds about 135 billion tons of ice per year and Greenland about 266 billion tons per year, reshaping coastlines and exposing new rock terrain underneath.
Elevation Extremes
The highest point above sea level is Mount Everest, at 8,848 meters (29,029 feet), straddling the border of Nepal and Tibet. The lowest point on dry land is the shore of the Dead Sea, sitting about 430 meters below sea level. Underwater, the Mariana Trench in the western Pacific plunges to nearly 11,000 meters (about 36,000 feet) below the surface. If you placed Everest at the bottom of the Mariana Trench, its peak would still be submerged by more than a mile of water.
How Earth’s Terrain Formed
Nearly all of Earth’s large-scale terrain features trace back to plate tectonics. The planet’s outer shell is broken into a dozen or more rigid slabs called tectonic plates that drift on top of a hotter, more fluid layer of rock beneath them. Where plates pull apart, molten rock wells up to create new crust, forming features like the mid-ocean ridge. Where plates collide, one often sinks beneath the other in a process called subduction.
Subduction drives mountain building in a powerful way. As an oceanic plate sinks, it releases fluids that melt the overlying rock, generating pockets of magma. Most of that magma cools deep underground, forming the granite cores of mountain ranges like the Sierra Nevada and the Andes. Some reaches the surface as volcanic eruptions, building volcanic ranges like the Cascades in the Pacific Northwest or the massive plateaus of the Columbia River region, where layer upon layer of lava flows stacked up over millions of years.
Working against this constructive force is erosion. Water, ice, wind, and gravity constantly wear down elevated terrain, carving valleys, canyons, and plains. Rivers cut through rock over millennia to create features like the Grand Canyon. Glaciers grind across landscapes, scooping out U-shaped valleys and depositing ridges of debris. The terrain you see at any given moment is the net result of building forces pushing rock up and erosive forces wearing it down.
How Humans Have Changed the Terrain
Human activity now physically reshapes Earth’s surface at a scale that rivals natural geological processes. Agriculture is the biggest modifier, converting forests and grasslands into cropland across every inhabited continent. Urbanization paves over natural terrain with concrete and asphalt, creating a surface that behaves completely differently from the soil and rock it replaced. Mining strips away entire hilltops and excavates pits that can be visible from space. Dams reshape river valleys into artificial lakes, and road networks fragment terrain across millions of kilometers.
These modifications are not evenly distributed. Europe and Asia show the heaviest transformation, while remote regions of Antarctica, the deep Sahara, and the Amazon interior remain closer to their natural state. The net effect is that a significant fraction of Earth’s land surface now looks and functions differently than it did even a few centuries ago, with ongoing changes tracked by satellite monitoring systems.