"Chapter 1 Summary - DOC"
Chapter 1 Summary Section 1.1 Earth’s atmosphere supports life. Pages 9-15 1. The atmosphere makes life on Earth possible. a. The atmosphere is a whole layer of air that surrounds Earth. It supports and protects life in several ways, such as by i. Absorbing harmful radiation ii. Maintaining Earth’s temperature iii. Providing elements essential for life b. The atmosphere has chemical and physical properties. i. The density of the atmosphere decreases with altitude. ii. Density is the amount of mass in a given volume of a substance. iii. Altitude is the distance above sea level. iv. The composition of the atmosphere is mostly Nitrogen gas (78%) and Oxygen (20%) with gases argon, carbon dioxide, and water vapor making up the rest. v. The amount of water vapor in the atmosphere at any given moment varies greatly, more so than the other gases. 2. Natural processes modify the atmosphere. a. Living things take part in cycles, or repeating processes, of gas exchange with the atmosphere. There are three main cycles. i. In the carbon cycle, plants take in carbon dioxide from the air and release oxygen during photosynthesis. During respiration, both animals and plants use oxygen and release carbon dioxide and water into the air. ii. In the nitrogen cycle, bacteria convert nitrogen gas in the atmosphere into solid forms and solutions. Animals and plants use these forms of nitrogen and when they decay, it is released back into the soil and then into the atmosphere. iii. In the water cycle, water is constantly circulated between Earth’s surface and the atmosphere by evaporation, condensation and precipitation.