1. Chapter 1 Section 1 Planet of Life

2. Earth is one of the nine planets in the solar system. Earth is the third planet from the sun. Mercury, Venus, Earth and Mars are known as the inner planets and are made mostly of rock. The other five planets are the outer planets and are made of mostly gases, with the exception of Pluto, which is rocky like the inner planets. Earth is the only planet to support life or living things called organisms.

3. The lithosphere is the layer of land that forms Earth’s surface and includes rocks, soil, and sand. The hydrosphere includes all the parts of the Earth that are made up of water and includes oceans, lakes, rivers and underground water and clouds in the air. The atmosphere is the layer of air that surrounds Earth.

4. One of the most important reasons Earth can support life is the presence of liquid water. Although water exists elsewhere in the solar system, it is usually in the form of ice or vapor. On Earth, liquid water in the hydrosphere stores heat. Water absorbs heat during warm periods and releases it during cold periods.

5. Another reason Earth is able to support life is its atmosphere. Air is a mixture of gases, including nitrogen, oxygen, carbon dioxide, and water vapor. Most organisms require oxygen to use energy. Plants require carbon dioxide to help capture and store energy from the sun. Almost all energy used by organisms comes from the sun and travels in the form of waves.

6. Each type of wave has a different range of wavelengths. Most waves are invisible. Waves in narrow range of wavelengths, called the visible spectrum, can be seen by the human eye.

7. Interactions among living and nonliving parts of the Earth are the subject of ecology. Ecology is the study of Earth, the home of living organisms.