Fossils

Fossils
How do organisms become preserved as fossils?
-A
fossil
is the trace or remains of an organism that lived long ago.
-Fossils are most often preserved in
sedimentary
rock.
-Fossils form in different ways.
Ways fossils form:
1. Trapped in amber
2. Trapped in asphalt
3. Buried in rock
4. Preserved in ice
5. Petrified
Trapped in Amber
-
Amber
is formed when hardened tree sap is buried
and preserved in sediment.
-Some of the best
insect
fossils are found in amber.
-Fossil spiders, frogs, and
lizards
have also been found
in amber.
Trapped in Asphalt
-There are places where
asphalt
bubbles up at Earth's surface in thick, sticky pools. (La Brea Tar Pits, California)
-These asphalt pools have trapped many fossils over the past ~
38,000
years.
-Fossils like these have revealed a lot about the past environment of California.
Buried in Rock
-When bodies are quickly buried in sediment, the process
of decay is slowed.
-
Hard
parts of organisms, such as
shells
and
bones
, are protected from decomposition, and preserved in the rock.
Preserved in Ice
-
Cold
temperatures slow down decay.
-Many types of frozen fossils are preserved from the
last
ice age
.
-Fossils that are frozen can include
skin
,
bones
, and
sometimes even
fur
.
-Sometimes the organism is fully intact.
Petrified
-After an organism dies, its tissues can be replaced by minerals. This process is called
petrification
.
-Petrification occurs in hard tissue, such as bone.
-It also occurs in
plant
tissues.
-Petrified wood looks like wood, but it is made of stone. The organic material has been replaced with the mineral
quartz
.
Trace Fossils
-
Trace
fossils are fossils that show the activity of an animal or plant but is not formed by the organism itself.
-Tracks, or
footprints
, are one type of trace fossils. They reveal a lot about the animal that made it, such as its size, how fast it was moving, and which direction it was headed.
Other Trace Fossils
-
Burrows
are shelters made by animals, such as clams on the sea floor or rodents on land, that dig shelters in sediment.
-
Coprolites
are trace fossils made from preserved animal dung. They tell scientists what an animal ate.
What do fossils tell us about Earth's changing environments?

Turn to page 333 in your book.