October 13, 1999
When it's underwater?
There are not many times when a feather weighs more than a birdunless the feather is ancient and has become a fossil.
Fossils are traces of past life. A typical fossil is a special kind of rock that forms when an animal dies and then gets buried in mud. If the animal goes undisturbed for a long time (hundreds of thousands of years or more), then its molecules are slowly replaced, one by one, with minerals from the water in the mud. Eventually, the animal's remains become mostly made up of minerals. Rock is made of minerals, so the animal has literally turned to stone!
This process of fossil formation is called permineralization. Plant parts also can become permineralized, and fossils can even form when mud fills a footprint or covers a feather. If this mud turns to stone, then the outline of the footprint or the feather is a fossil, too.
By studying fossils, scientists learn about the history of life on Earth. For example, many animals have come and gone on Earth, and we know about them from the traces they leave behind as fossils. This is called the fossil record. Fossils can tell us how ancient plants and animals interacted with one another, how they lived in their environments, and even how they changed over time. Fossils of sea creatures, for example, have been found throughout Texas; these fossils mean that Texas was once underwater! As you can see, paleontologists (scientists who study fossils) have taught us a lot about our Earth.