This part of the Rocky Mountain Range in the Yukon Territory of Canada is an excellent example of mountains on Earth. These mountains are so remote and rugged that ground surveys of the area are very expensive. Due to remote-sensing techniques developed for planetary exploration, many such areas can now be observed and studied from space at much less cost and effort. This space shuttle view of the Atlantic Ocean and Mediterranean Sea illustrates an important feature of Earth-a seacoast. Earth is the only planet with borders of land adjacent to bodies of water because it is the only planet where liquid water is stable at the surface.
Seas are important because water has been the catalyst for the development of life on our planet.
The Strait of Gibraltar is the border between Africa and Europe. This view over St. Louis, Missouri, taken in June 1991, shows the Mississippi just left of center. These scars are visible in the river bottom land between the cliffs on either side of the river. This space shuttle image of the Colorado River in Arizona captures the Grand Canyon. The Grand Canyon was created by the erosional action of the Colorado River on the surface as this region has continued to rise high above sea level over the last several million years.