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How long does it take for bones to become fossilized?
Mark and Mike sit in front of a large fossil still in the ground.
Luckily, this fossil of an ankylosaur that Mark and Mike Novacek found in the Gobi desert made it through the fossilization process and survived in one piece.
 

Not all fossil bones are alike. Some fossil bones that are 60 or 70 million years old have a lot of their original chemical composition - they almost seem more like bone than rock. Other fossil bones could be "just" 10,000 years old, but they're so hard you could drive nails with them. How long it takes depends on the conditions the bone is buried in. Here's a tip. When you find a fossil bone, you already know something about the animal. You know it must have been buried very quickly. Why? Bones left exposed for long would decay. After an animal is buried, the specific conditions of the local environment come into play.