Fossils
Pgs. 106G – 112G
8-2.2: Summarize how scientists study Earth’s past
environment & diverse life-forms by examining
different types of fossils (molds, cast, petrified,
preserved fossils & carbonized remains of plants &
animals and trace fossils.)
Fossils
• Fossils are preserved remains or traces of
living things.
• Most fossils form when living things:
1. die
2. buried by sediments quickly.
3. bones are replaced by minerals.
4. sediments slowly harden into rock and
preserve the shapes of the organisms.
Can all dead things become a fossil?
Types of Fossils
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Mold
Cast
Petrified
Preserved
Carbonized
Trace
Mold Fossil
• A mold is a hollow area in sediment in the
shape of an organism or part of the
organism.
• Forms when sediments bury an organism
and the sediments change into rock.
– The organism then decays leaving a cavity in
the shape of the organism
Cast Fossil
• Cast is a copy of the shape of an
organism.
• Forms when a mold is filled with sand or
mud that hardens into the shape of the
organism.
Website
• http://www.classzone.com/books/earth_sci
ence/terc/content/visualizations/es2901/es
2901page01.cfm?chapter_no=visualizatio
n
Petrified Fossils
• Forms when minerals soak into the buried
remains, replacing the remains and
changing them into rock.
• Petrified fossils are fossils in which
minerals replace all or part of the
organism.
– Petrified means “turning into stone.”
Preserved Fossils
• Forms when entire organisms or parts of
organisms are trapped in ice, tar, or amber
and are prevented from decaying.
- Iceman found in ice
- Amber – insects stuck in the sap
- Tar – animals get stuck in tar and die.
ICE MAN: preserved in ice
Ötzi the Iceman (pronounced
[ˈœtsi] (help·info)), and
Similaun Man are modern
names of a well-preserved
natural mummy of a man from
about 3300 BC (53 centuries
ago).[1] The mummy was found
in 1991 in the Schnalstal glacier
in the Ötztal Alps, near
Hauslabjoch on the border
between Austria and Italy. The
nickname comes from Ötztal
(Ötz valley), the region in which
he was discovered. He is
Europe's oldest natural human
mummy, and has offered an
unprecedented view of
Chalcolithic (Copper Age)
Europeans.
AMBER: insects
preserved in sap
from a tree.
TAR: animals fall into tar pits and are buried like saber-toothed cats
and mammoths.
http://blackhills360.com/bhgalleries/mammogallery.html
Carbonized Fossils
• Forms when organisms or parts, like
leaves, stems, flowers, fish, are pressed
between layers or soft mud or clay that
hardens squeezing almost all of the
decaying organism away leaving the
carbon imprint in the rock.
• Carbon fossils are a thin coating of carbon
on rock.
Undetermined Leaf Henefer
Formation, Cretaceous, Coalville,
Summit Co., Utah
Crossopteris utahensis Fern
Leaf, Manning Canyon
Formation, Pennsylvanian, Lake
Mountains, Utah Co., Utah
Ginko Leaf Paleocene,
Morton Co., North Dakota
Macginetea Sycamore leaf,
Green River Formation,
Eocene, Douglas Pass,
Colorado
Rhodea Fern Leaf, Manning Canyon Formation, Pennsylvanian,
Lake Mountains, Utah Co., Utah
Trace Fossils
• Form when the mud or sand hardens to
stone where a footprint, trail, or burrow of
an organism was left behind.
• Provides evidence of the activities of
ancient organisms.
– Size and behavior
– Did it walk on two or four legs?
– Did it travel alone or with others?
– ……..
Megalosaurus footprint - A meat eating predator from the Jurassic