"An archaeologist working in Egypt discovers the portrait of a pharaoh's daughter on a tomb wall, and announces quite confidently that it must have been carved in 1360 B.C.—
"A paleontologist digs the skeleton of a dinosaur out of the side of a Wyoming cliff, and tells reporters that the giant beast lived about 120 million years ago—
"An astronomer, after analyzing a meteorite that has fallen in Alaska, says that it confirms his belief that our world was formed some 4.6 billion years ago—
"How do they know?" asks Robert Silverberg. "What evidence doscientists have, really, when the so glibly rattle off the dates that we customarily take for granted?"
The evidence may be the color of a bit of broken pottery, the direction which a shell coils, the number of rings in the stump of a tree, the radioactive content of a piece of rock. The span of time under study may be billions of years or just a few centuries. But through the use of a variety of remarkable techniques, perfected in the last hundred years, scientists are now able to assign astonishingly precise ages to almost everything from an old Indian sandal to the stars in the sky.
In a book as exciting and absorbing as a detective story, Robert Silverberg explores the ways in which these analytical techniques were developed and how they are being used to uncover the secrets of the past.