FOSSIL

F&Q

SOME FACTS

When people think of fossils, most people think of dinosaur fossils or a leaf imprinted into a cement path walking out of school. But there are many types of fossils. These types are molds, casts, trace fossils, and petrified fossils. A mold is an imprint of anything in a rock, or any surface. It is like the leaf that you see imprinted in the cement on your way out of school. A cast is when there is a replica of that mold that is 3D, and has most of the features. Trace fossils are basically what they say, fossils showing the traces of anything, like a footprint. When that is preserved in the ground, it is a trace fossil. A petrified fossil is when some or all of a fossil is replaced with a mineral. Sometimes, when you go to a museum, and you see some discoloration in a fossil, that is a petrified fossil. A regular fossil is the fossil that you see in a museum with no discoloration at all.

CASTS AND MOLDS

Casts and molds normally form together. The mold is imprinted when the cast, which is 3D, pushes into a rock, forming a mold. They are typically formed in plain rock. Casts are rare on the surface, because pressure has to push it down, so they normally form underground. The main rock you will find a mold on is a soft rock, because then there doesn’t have to be a ton of pressure to imprint the image.

TRACE FOSSILS

Trace fossils aren’t rare. Most people have seen a trace fossil in their lives. They are commonly found in muddy areas. When you step mud, and you get mud all over your shoe, you may not realize it, but you made a trace fossil. The most common trace fossils are dinosaur trace fossils because they were heavy enough to imprint the ground and have had time to preserve the traces.

PETRIFIED FOSSILS

A petrified fossil is very hard to find, but they are more common than regular fossils. Petrified fossils are normally found deep underground, where the minerals are. Fossils are fragile to chemical reactions, so the chemical reactions can cause some of the minerals to form inside of the fossil. Also, if the fossil is made inside a vain of anything, there is a good chance that the fossil will be a petrified fossil

QUESTIONS

What are the four types of fossils?

Mold, cast, petrified, and trace

What is a mold?

A mold is an imprint of a fossil in a rock

MORE QUESTIONS

Where do petrified fossils normally form?

Underground, near minerals

What is the most common trace fossil?

A dinosaur footprint

SITE

http://www.ucmp.berkeley.edu/paleo/fossilsarchive/casmol.html