Download Most fossils form from organisms buried in sediments soon after they

Fossil Notesheet Answer Key
from Earth’s Changing Surface pp110-113
A fossil is the remains or evidence of a living thing.
How does a fossil form? Most fossils form from organisms buried in sediments soon after they die. Quick burial in sediments
prevents animals from eating the dead organisms. It also slows down or stops decay.
Why are fossils usually found in Sedimentary rock? Sediments in the form of mud and sand could easily bury plants and animals
that died in or alongside the water. When the sediments slowly hardened and changed into rocks the organisms were trapped in
the rocks.
Where do most fossils form? Plants and animals that lived in or near water were preserved more often than other organisms.
Why do we usually only find the bones, shells, teeth, seeds and woody stems of an organism fossilized?
In many cases, the soft flesh of dead organisms was eaten by animals before the fossils formed. Also soft tissues of dead plants
and animals tend to decay before fossils can form.
Fossil Type
How does it Form?
Molds and Casts
These form when an animal or plant is buried in
sediments that harden into rock. If the soft parts of
the organism decay and the hard parts are
dissolved by chemicals, an empty space will be left
in the rock. That empty space is called a mold. If
the mold fills with minerals these harden to form a
cast in the same shape as the original organism.
Draw a picture to illustrate
This is a mold fossil
This is a cast fossil
Fossil Type
How does it Form?
Draw a picture to illustrate
Petrified Fossils
When minerals gradually replace the original substances of the plant or animal. Plants and animals also become petrified
when minerals fill in the air spaces of bones or shells and harden. The minerals show many of the details of the original plant
or animal. But the petrified fossil may take on the color of the minerals that replaced the plant or animal remains.
Carbon Films
A carbon film is an extremely thin coating of carbon on rock.
When sediment buries an organism, some of the materials that
make up the organism evaporate or become gases. These gases
escape from the sediment leaving carbon behind. Remember all
living things contain carbon
Trace Fossils
These fossils are the marks or evidence of the activities of an
organism. Such as footprints, trails and burrows.
Amber, Tar or Ice
When a resin from certain evergreen trees hardens, it forms a
hard substance called amber and when flies or other insects
become trapped in the sticky resin it hardens around them.
Similarly animals trapped in tar pits can become fossils. The
animals sink to the bottom of the tar pit and usually only bones
are found. But whole furry rhinoceroses have been found in tar
pits in Poland.