• Aim: how do I identify different
types of fossils?
• Engagement:
– Look at the following picture and
answer the included questions
Shown here
is a special
type of tree
remains
called
“petrified
wood”
1. What do you think these remains are made of?
2. How do you think they were made?
3. Are there other objects we study that form in
similar ways? What are they called?
Formation of Fossils
• Fossils are the remains, imprints, or
traces of prehistoric organisms.
• Fossils are
evidence of
not only when
and where
organisms
once lived,
but also how
they lived.
How fossils are formed
Write this list in your notebooks and leave
some lines between each word!
•Permineralized remains
•Carbon films
•Molds and casts
•Original remains
•Trace fossils
Permineralized remains
•Permineralized remains are fossils in which
the spaces inside are filled with minerals from
groundwater.
•Sometimes minerals replace the hard parts of
fossilized organisms.
•For example, a solution of water and dissolved
silica might flow into and through the shell of a
dead organism.
Carbon Films
• Upon death, a plant can be buried in
sediment, and most of the organic materials
are removed.
• A thin film of carbon residue is left, forming
a silhouette of the original organism called
a carbon film.
Molds and casts
• Impressions form when seashells or
other hard parts of organisms fall into
a soft sediment such as mud.
• Over time, the mud is compacted and
cemented together, forming
sedimentary rock.
• The hard part of the organism might
decay or dissolve, leaving behind a
cavity in the rock called a mold.
• Later, mineral-rich water or other
sediment might enter the cavity, form
new rock, and produce a copy or cast
of the original object.
Original remains
• Sometimes, an entire organism
can be preserved in materials
such as amber (fossilized tree
sap) or ice.
Trace fossils
• Also, tracks can be fossilized and
can teach us about animals.