IT’S ABOUT TIME Kids always know how old they are That is because they know their birthday and it’s easy to keep track by counting the years as they go by Knowing the age of our planet is not so simple For one thing the history of Earth is far longer than the history of human beings living on it Scientists study rocks to learn how old the Earth FIELD NOTES Scientists study rocks to learn how old the Earth might be Human beings rarely live to be more than might be Human beings rarely live to be more than 100 years old Though a century is a long time for a 100 years old Though a century is a long time for a human to live it is little more than a blink of an eye human to live it is little more than a blink of an eye when considering the age of the planet itself when considering the age of the planet itself 4
Time is relative To a kid a year seems like a mighty long time to wait for a present or a vacation But to the Earth a year is like a split-second Compared to an individual person or even compared to the human race Earth is unimaginably old The study of the Earth itself what it is made of and all that lies beneath the ground is the science of geology Geologists call the ground we walk on Geologists call the ground we walk on Earth’s crust Like a pie crust Earth’s outermost layer is a thin shell which is even thinner under the ocean and thicker where there is dry land 6
