February 27, 2008

Fossils Aren’t Simply Bones or Impressions

Many people believe fossils are petrified bone or impressions of a shell in rock. But fossils actually are any type of evidence of the existence of a once-living organism - plant or animal.

Accurately dating the age of the Earth is commonplace today. Take a few rocks, analyze them on fancy machines, and presto, out pops the Earth's age.

But these techniques are not new. A century ago, B.B. Boltwood outlined the basics.

Boltwood got his doctorate from Yale University in 1897. A decade later, he was back as professor of physics. In 1907, he published a list of geologic ages - time spans for ancient rock formations.

His dates have been revised since, but the U.S. Geological Service says Boltwood was right saying the age of the oldest rocks would be "hundreds to original material, unaltered, or as shells in rock, or as impressions of shells in rock after the actual shell is dissolved.

There is another category of fossil called "trace fossils." These consist of evidence that an animal existed even though there are no remains, such as bones or shells, of the animal itself. Such evidence can come in the form of tracks or burrows.

In Virginia, no dinosaur remains have been found, but we know they existed because of dinosaur tracks in areas such as Culpeper County.

Soft-bodied invertebrates such as worms are not preserved, but their homes, in the form of burrows, are commonly preserved. Some of the oldest fossils in Virginia are burrows named "Skolithos" found in Cambrian sandstone that are about 510 million years old.

So why are fossils important? What can we learn by studying fossils? Fossil research can answer questions we want to know about animals of the past.

We could find answers to questions such as: What species of animals existed? What did they eat? How did they get food? Where did they live? How did they care for their young?

We now know that fossils are more than just bones; instead, there are many different forms of fossils. Parts and pieces, feces and trails, fossil bits become the gold coins that frequently buy scientists a trip back in time.


On the Web

The Museum of Natural History Nova Scotia: http://museum.gov.ns.ca/mnh/nature/tracefossils/english/

University of California at Berkley:


Correlated Virginia science Standards of Learning: K.9; 1.8 a; 4.8 b; 5.7 b; LS.14 b; ES.10 a, d.

Lauck W. Ward is curator of invertebrate paleontology at the Virginia Museum of Natural History in Martinsville.