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What is a Fossil?

January 19, 2013

Hi, I’m Emerald Robinson, and in this “What Is” video, we’re going to investigate pieces of our past called fossils.

Many of us think of fossils as just the remains of dinosaurs. In order to qualify as a fossil, an object must be at least several thousand years old, but the oldest fossils have been determined to be about three and a half billion years old.

Paleontologists, the scientists that study prehistoric life, define a fossil as any type of physical evidence of ancient life.  Fossils can be tracks left behind by an animal, impressions of plant leaves in a rock, ancient burrows and dens, or an entire insect perfectly preserved in tree sap that has crystallized into amber.

Skeletal fossils are made when an animal dies, and are buried very quickly beneath layers of fine rock and dirt called sediment. Decomposers like bacteria and fungi break down the animal’s skin, muscle, and organ cells, leaving just the bones. Over time, many more layers of sediment accumulate on the skeleton, causing pressure to squeeze out any water left in the bones, and to fill in any spaces with minerals. This process, called “lithification,” results in the stone skeletons we see in museums.

Since plants don’t have a skeleton, it’s much rarer to find a preserved plant. Instead, plants tend to leave a type of fossil called an impression. An impression forms in much the same way as a bone fossil, except that as the plant decomposes, it leaves a leaf print embedded in the rock.

We’ve been able to find fossils that have been buried for millions of years because the Earth’s geology is constantly changing. Fossils have given us valuable clues to the earth’s past. And who knows what’s still buried for us to find?



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