Planet Earth Chapter 2
2.3 explain how the relationship between Earth and Sun is critical to the study of geography Our solar system • The sun is at the center of our solar system. It exerts a strong force of gravity that keeps Earth and all the other objects in the solar system revolving around it
The Planets: Neighbors in Space The largest objects that orbit the sun are called planets. At least nine planets orbit our sun. Some of the planets have one or more moons. Mercury, Venus, Earth, and Mars are terrestrial planets because they have solid rocky crusts.
Farther from the sun are the gas giant planets–Jupiter, Saturn, Uranus, and Neptune. • They are much more gaseous and less dense than the terrestrial planets. • Pluto, the exception among the planets, is a ball of ice and rock.
2.1 explain internal and external physical forces that impact Earth Asteroids, Comets, and Meteoroids • Smaller objects in the solar system include asteroids, comets, and meteoroids. • Asteroids are small, irregularly shaped, planet-like objects. • Comets are made of icy dust particles and frozen gases. Meteoroids are pieces of space debris–chunks of rock and iron.
Getting to Know Earth • Earth is the largest of the inner planets. Its diameter at the Equator is larger than the diameter from pole to pole. Water, Land, and Air • The surface of the earth is about 30 percent land and about 70 percent water. • The atmosphere is about 78 percent nitrogen, about 21 percent oxygen, and about 1 percent other gases, such as argon.
Landforms • The earth’s landforms–physical features of particular shape and elevations–include continents, mountains, hills, plateaus, valleys, and plains. • The part of a continent that extends underwater is called a continental shelf.
Earth’s Heights and Depths • The highest point on Earth is the summit of Mount Everest at 29,035 feet (8,852 m) above sea level. • Earth’s lowest point of dry land is on the shore of the Dead Sea at 1,349 feet (411 m) below sea level. • The deepest known level of the ocean floor is the Mariana Trench at 35,827 feet (10,923 m) below sea level.