Don't Know Much About Planet Earth

Don't Know Much About Planet Earth


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Product Details

ISBN-13: 9780064408349
Publisher: HarperCollins Publishers
Publication date: 07/24/2001
Series: Don't Know Much About Series
Pages: 144
Product dimensions: 6.00(w) x 9.00(h) x 0.40(d)
Age Range: 8 - 12 Years

About the Author

Kenneth C. Davis is the New York Times bestselling author of A Nation Rising; America's Hidden History; and Don't Know Much About® History, which spent thirty-five consecutive weeks on the New York Times bestseller list, sold more than 1.6 million copies, and gave rise to his phenomenal Don't Know Much About® series for adults and children. A resident of New York City and Dorset, Vermont, Davis frequently appears on national television and radio and has been a commentator on NPR's All Things Considered. He blogs regularly at

Read an Excerpt

Chapter One

What's So Special About Earth?

What in the world is geography?

Geography is the science that explains why you -- yes, you reading this book -- are where you are. It asks and answers some of humankind's most basic questions: Where am I? What's over there? How did it get there? What is it like? Why is it there?

Geography is the big mixing bowl of the sciences: it brings together all sorts of other specialties. If you combine a little history, geology, meteorology, biology, economics, astronomy, and almost every other "ology", "onomy," or "omics" you can think of, you'll begin to see what geographers do. They study how we shape -- and are shaped by -- the shape of the world.

Has Earth always been around?

It has always been a fairly round planet. (It does bulge a little in the middle.) But Earth hasn't always been around. Earth and its neighboring planets started out as a huge cloud of space dust and gas. Then, about 4.6 billion years ago, something -- maybe a shock wave from a nearby exploding star -- gave the cloud a push, and it began spinning into a flat disk. Gravity pulled some of the dust and gas toward the disk's center. There it clumped into a dense and intensely hot ball of gases and the Sun was born. Most of the other dust and gas formed smaller, cooler clumps that became Earth and the other planets, moons, asteroids, and comets that travel around the Sun as our solar system.

What's so special about Earth?

Of the nine planets in our solar system, Earth is the only one (that we know of) that has life. As the third planet from the Sun, Earth gets just the right amount of heat to keep water in its three forms -- liquid, vapor, and ice -- and to support our kinds of plants and animals. Earth's atmosphere, the blanket of air that surrounds it, is also unique. It contains oxygen for us to breathe, protects us from the Sun's heat and harmful rays, and keeps our planet warm.

How is Earth like a peach?

Earth might not look or taste like a peach, but the two do have a few things in common. Like a peach, Earth has a thin outer skin. This is -- Earth's crust. Underneath Earth's crust is the juicy fruit, or mantle. The mantle is a thick layer of really hot rocks and goopy semimelted rock called magma. Underneath the mantle is the peach pit, Earth's core, a solid, superhot ball of iron. Now imagine that the skin of our peachy Earth has been sliced into sixteen or so irregularly shaped pieces. All these separate pieces, or plates, float around the outside of Earth like giant rafts on a sea of molten rock.

230 million years ago, you could have walked from Pole to Pole.

True! Back then, all Earth's land was connected in a huge single mass called Pangaea ("all land" in Greek). So what happened between then and now? Earth's plates have been on the move in a process called plate tectonics. Even though most plates move only a few inches a year, those few inches add up over millions of years. In time, continental drift tore Pangaea apart to form the continents and islands we know today. If you look closely at a map of the world, you can see how the edges of some continents, such as South America and Africa, could still fit together like the pieces of a jigsaw puzzle.

The continents continue to move, about 1/3 inch to 6 inches (3/4 cm to 15 cm) a year. In another few million years, East Africa will probably break off from the rest of Africa, and Mexico's Baja California peninsula will detach from North America.

Earth's plates drift around so slowly that we usually don't know they're moving. But where plates grind into each other or pull apart, there are scenes of slow violence. Sometimes this violence bursts onto Earth's surface when earthquakes rattle our houses, volcanoes erupt, or mountains rise from flat land.

Does everyone agree that there are seven continents?

No. A continent is simply defined as one of the main landmasses on the planet. This definition is a problem when you look at Europe and Asia, because they're one big landmass. That's why some geographers say Europe and Asia are one continent, Eurasia, so that there are only six continents, not seven. (We'll discuss this more in Chapter 6.) But since continents are a way to help us organize and refer to the world's many different lands and peoples, it's usually more useful to say there are seven: Asia, Africa, North America, South America, Antarctica, Europe, and Australia.

Whose fault are earthquakes, anyway?

If you asked the ancient Japanese, they'd blame the thrashing namazu, a giant catfish believed to live underground. Sound a little fishy? Middle Eastern tribes were sure the shaking of Earth was a sign of God's displeasure. Today we know that earthquakes happen after Earth's plates build up pressure by pushing into or squeezing past each other. When the plates can't take the pressure anymore, they release the stress by slipping suddenly along faults, or cracks in Earth's surface. When the rocks along a fault move quickly, they send out ripples, or shock waves, through the ground. The ground moves up and down and side to side, turning what once seemed like a solid surface into a bowl of quivering Jell-O.

Do high tides bring high tidal waves?

A tidal wave is more properly called a tsunami, which is a Japanese word for "harbor wave." Tsunamis have nothing to do with tides, but a lot to do with earthquakes. Quakes under the ocean floor can create these enormous, fastmoving waves that can travel great distances and crash down on people and cities along the coast.

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