Earth and the Terrestrial Worlds
This Chapter focused on Earth in relation to the other planets. Earth has gone through tremendous changes since the beginning of its existence. The surfaces of all five terrestrial planets (Mercury, Venus, Earth, the Moon, and Mars) would have looked similar before all of these changes. Because these planets are similar, we are able to group them together in a category called the Terrestrial planets.
The interior structure of these terrestrial planets is usually a high density material, with a mantle following that, and a low density crust. The surfaces of these planets are shaped by impact craters, volcanoes, tectonics, and erosion. Virtually all geological features originate from impact cratering, volcanoes, tectonics, and/or erosion. Earth's atmosphere and oceans were made from gases released from the interior by volcanic out gassing.
The Earth's atmosphere is greatly affected by greenhouse gases. The ozone absorbs the Sun's dangerous ultraviolet radiation, while the X rays are absorbed by the atoms and molecules higher up in Earth's atmosphere. The greenhouse affect is allowing the surface of the Earth to become much warmer than it would stay otherwise, which is also having other effects on the Earth.
We have also learned more about the moon over time. We now know that the geological features of mercury are similar to our moons features, and that there are many craters on the moon.
The chapter also discussed Mars and the many changes that Mars is facing. The idea that Mars could have life on it is one common belief because Mars and Earth have similarities. Mars is quite different from Earth, however. Mars has extremely active volcanism in the past, and its surface is dotted with numerous large volcanoes. Dried up riverbeds and other signs of erosion show that water flowed on Mars in the distant past. When Mars lost most of its atmospheric carbon dioxide to space, it began to face changes that made it the planet it is today.
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