Throughout Earth's 4.5-billion-year history, the heat at its core has rearranged the surface over and over. The crust, the surface layer of the planet, has been compressed, pulled apart, raised, and lowered.
Canyons exist below the rim of the land, below the horizon. These ragged scars on the face of the planet descend hundreds to thousands of feet below their surrounding landscape, giving it depth.
They are beautiful and sometimes otherworldly. Existing beneath the surface of the planet, caves have attracted humans for hundreds of thousands of years.
Coasts mark the area where dry land meets oceans or other large bodies of water. They are one of the most active environments found on Earth.
They are the drowned edges of continents. Covered by the oceans, continental margins are part of the same crust (thin, solid outermost layer of Earth) that forms the continents.
Coral reefs are not only spectacular marine environments, but they are one of the oldest ecosystems (community of plants and animals interacting with their environment) on Earth. They are created by colonies of organisms called coral polyps (pronounced PAH-lips).
Deltas have long played an important role in human history. These fertile areas where rivers flow into large bodies of water have served as fishing, farming, and living sites.
Desert environments have fascinated humans throughout the ages. Covering approximately one-third of Earth's land surface, these arid (dry) landscapes receive less than 10 inches (25 centimeters) of rain per year and support only limited plant and animal life.