A Wonderful Home Earth is a wonderful home for living organisms. A great variety of organisms live here. They benefit from abundant water, a thick atmosphere, and Earth s suitable distance from the Sun. Scientists have studied the other planets and the many moons of the solar system. None possess the properties that would allow them to support life as Earth does. 1 Why is Earth s distance from the Sun important for living organisms? 2 Look at the photo. What properties of Earth are shown? 3 Are living organisms found in all parts of Earth? Discuss. Bellringer LESSON 1X
Distribution of Earth s Water Salt water (oceans) 97% Total water on Earth Freshwater 3% Groundwater 20% Ice caps and glaclers 79% Fresh surface water 1% Rivers 2% Swamps 11% Freshwater Lakes 87% Fresh surface water Focus on Content LESSON 1
Neighboring Lands Neighboring lands do not always look alike. Lake Tahoe lies on the border between California and Nevada. Surrounding the lake are mountains covered thickly with trees. Southeast of the lake, however, lies a vast desert. Here sagebrush and cactuses grow in dry, sandy soil. 1 What do the photos reveal about the weather around Lake Tahoe and in the desert? 2 The Truckee River flows out of Lake Tahoe, and water also leaves the lake by evaporation. Why doesn t the lake lose most of its water? 3 Look at the photo of the desert. Does it ever rain here? How can you tell? Bellringer LESSON 2X
Rain-Shadow Effect Rain shadow Wind Coast Range Windward (wet) Sierra Nevada Leeward (dry) Great Basin Focus on Content LESSON 2
Teacher Guide Lesson 1 Bellringer Medioimages/PunchStock A Wonderful Home Earth s two neighboring planets, Mars and Venus, both have rocky surfaces surrounded by an atmosphere. But neither planet currently has water in the liquid state, and thus they cannot support life that is in any way similar to living organisms on Earth. Earth has not always had the range of temperatures that are common today. The very young Earth was extremely hot, and then it cooled off gradually as its atmosphere formed. More recently in geologic history, cold temperatures caused ice caps to expand and glaciers to advance across much of Earth s surface. Answers to Questions 1 All living organisms depend on liquid water, and water exists as a liquid only within a certain range of temperatures. Temperatures would rise if Earth were closer to the Sun and would fall if Earth were farther away. 2 Possible answer: The river and snow show that Earth has water in the liquid and solid states, and it can be inferred that water vapor is part of the atmosphere. The trees and geese show that Earth is home to living organisms. 3 No, living organisms are concentrated in only a small region of Earth. Earth is a sphere in space with many layers. All living organisms live on or near Earth s surface or in its oceans. Lesson 1 Focus on Content Distribution of Earth s Water Although much of the planet is covered with water, freshwater remains a precious resource in many places. The first graph shows that only 3percent of Earth s water is freshwater. The second graph shows the sources of freshwater and that only 1percent is easily accessible on Earth s surface. The third graph shows these accessible sources, which include lakes, rivers, and swamps. Lesson 2 Bellringer (t)digital Vision/PunchStock; (b)u.s. Fish & Wildlife Service/J & K Hollingsworth Neighboring Lands The transparency illustrates the significance of the water cycle. In the mountains around Lake Tahoe, regular precipitation fills the lake and supports the growth of dense forests. In the desert, lack of precipitation keeps the plants short and less massive and the soil sandy. Answers to Questions 1 The photo of Lake Tahoe reveals that the area receives enough precipitation to support a forest and a lake, and that the winter weather on the mountain peaks is cold and snowy. The photo of the desert shows cactuses, sagebrush, and sandy soil, all of which suggest hot, dry weather. 2 Rain and snow add water to the lake, as does melted snow that flows as runoff from the nearby mountains. Groundwater also seeps into the lake from underneath. 3 Rain occasionally falls in the desert shown in the photo. The cactuses and sagebrush need some water to survive. Lesson 2 Focus on Content Rain-Shadow Effect The desert to the east of the Sierra Nevada is a classic example of the rain-shadow effect. Moist air blows east from the Pacific Ocean to the mountains. The water vapor cools and condenses as the air rises up the mountain slopes, then falls as precipitation. This leaves little water in the air that reaches the leeward side of the mountains where the desert lies.