Earth’s Inhabitants Are Young CONTENTS Introduction Earth Is Big Earth Is Small Earth Is Old Earth Is Cold Earth Is Hot Earth Is Wet Earth Is Dry Earth Is Fast Earth Is Slow 4 6 8 10 12 14 16 18 20 22 24 2
Earth Is Round Earth Is Jagged Earth Is Heavy Earth Is Light Earth Changes Quickly Earth Changes Slowly Is Earth Ours Earth Is Unique Glossary Index Source Notes 26 28 30 32 34 36 38 40 42 44 46
INTRODUCTION The Earth is our home the only place we humans have ever lived and for most of our history the only place we knew existed But once we began to study outer space we also started to discover that our planet is just one of many in the universe Since then we have ventured out into space and looked back at Earth from afar like a big blue ball in a sea of black The images from space have made us keenly aware of something as big as Earth seems to us here on the surface our planet is really tiny compared to the vastness of space Even so our home planet is quite different from the rest of the known worlds in our solar system Over billions of years different processes have shaped and molded it into a home like no other One of the best ways to get a better understanding of our home sweet home is to find out how Earth and the things that live on it compare to the rest of the universe That’s what this book is all about The best way to compare two things is to measure them We humans like to measure things There’s something powerful about knowing how big how heavy or how fast something is and being able to compare a tortoise to a cheetah to a race car to a comet Once you get started measuring and comparing you’ll notice we do it all the time We measure the temperature outside on a warm summer day the pressure of the air in a perfectly inflated soccer ball and our own ages so we can compare them to the ages of our friends and family Measuring and comparing also lets you see things from different angles Our planet orbits the Sun at an average distance of about 93 million miles 150 million kilometers Is that far Well it depends what you compare it to It’s a lot farther than a snail can walk in an hour or even a lifetime but it’s much closer than Pluto 4
Is the Earth heavy Well yes It has a mass of approximately 6.6 sextillion tons 6 septillion kilograms That’s a 6 with 21 zeros after it That seems like an awful lot doesn’t it But when you look at how dense the Earth is how much mass fits in each bit of space all of a sudden Earth starts to look pretty light There are a lot of metals that are denser than Earth including familiar ones like iron and silver and gold In this book we explore our planet and a lot of other things through measurement and comparison To do that we use what are known as standards of measurement units we have all agreed to such as feet pounds meters kilograms tons and degrees This agreement is key If we were to measure distance for example by the number of steps it takes to travel it then my measurement and yours would be different because we take different sized steps That’s why people invented standard units Throughout this book we’ll explore a lot of different standards Some will be very familiar to you Others might be totally new But all of them are fun because they give you the power to understand the world around us So welcome to big small heavy light cold hot wet dry fast slow round jagged planet Earth a fantastic home by any measure A note on the measurements in this book Across the globe there are lots of different systems for measuring things But wherever you are scientists use what’s called the metric system and many countries do too The metric system uses standard units such as meters and kilograms for their measurements In this book you'll see both United States customary units and metric units Information on converting metric to United States customary units such as inches and pounds can be found on page 43 of this book 5
