Almost without our realizing it, the tools for space studies have brought about a new age of rediscovery of the planet Earth itself.Viewed from space, Earth presents a fascinating range of surface features (Figure 8.1).High-standing continents began to form at this time and were not recycled back into the mantle.
One of the most significant results of space exploration concerns our view of Earth and the dynamics of how the planet changes.Now, "for the first time in all of time man has seen the Earth from the depths of space---seen it whole and round and beautiful and small." With satellite photography Earth is seen literally from a new point of view and geology is perceived and understood in a new planetary perspective.Several complete cyclonic storms, spiraling over hundreds of square kilometers, can be seen pumping huge quantities of water from the ocean to the atmosphere.Much of this water is precipitated on the continents and erodes the land as it flows back to the sea.Most large-scale features such as the continents, ocean basins, mountain belts and volcanoes are the result of Earth's internal heat.
Small-scale features such as fluvial valleys, coastlines, and deserts, are directly or indirectly the products of the atmosphere and energy from the Sun.
To many, the breathtaking photographs of Earth from space may be simple items of great beauty, but to the student of geology they reveal much more than mere clouds, oceans, and continents.
These photographs tell us much about how the planet works as a dynamic system undergoing constant change. Earth, like the other rocky inner planets, is differentiated with a dense iron-rich core that is still partially molten, a thick mantle of iron- and magnesium-rich silicates, and a crust of silica-rich and magnesium-poor rocks. The present atmosphere contrasts sharply with those around other inner planets because it is poor in carbon dioxide, rich in the residual nitrogen, and also rich in oxygen. Earth's lithosphere is ten to several hundred kilometers thick and is thinner and more mobile than that of the Moon, Mercury, or Mars. The continents and ocean basins are the principal surface features of Earth.
By an alien scientist it might be called the Blue Planet; but the deserts, such as the Sahara, are distinctly orange and the lush vegetation gives the tropics a deep greenish hue.
Contrasting beautifully with the azure blue are the white streamers of clouds and the massive ice cap of Antarctica.
Repeated cycles of ocean basin formation and closing shaped the present appearance of the planet's surface.