Transcript Studying the Past - Seymour Middle School

Medora, ND
public fossil dig,
2005
Studying the Past
Chapter 29
Pages 646-663
Geology
fossils
• A fossil is any evidence of earlier life
preserved in rock.
• The study of the life the existed in prehistoric
times is called Paleontology
Types of fossils
•
•
•
•
•
Original remains
Replaced remains
Molds and casts
Trace fossils
Carbonaceous films
Original remains
• Rarely occurs where organism is
preserved in its entirety – before
they decay and rock forms around
them OR minerals are deposited
into porous areas of the bones,
teeth, shells, etc.
• Examples:
– Encased in ice
– Insects in amber
Replaced remains
• Organisms can be slowly
replaced by rock-forming
minerals.
– Bones, teeth, shells
• Sometimes groundwater
removed the original organic
material - completely
replacing them with
minerals.
– Petrified wood
Molds and casts
• After a replaced fossil forms – the
fossil may be later dissolved out
of the rock, leaving a hollow
depression called a mold.
• Minerals then may seep into the
mold and fill it, forming a cast or
copy of the original fossil.
• Examples:
– Shellfish, ferns, leaves, fish
Trace fossils
• Indirect evidence of an organism
or its activities
• Examples:
– Footprints, burrows, tracks, bite
marks, etc.
Carbonaceous films
• Sometimes only a
thin carbon film
remains (silhouette)
• High temperatures
and pressures may
cause chemical
changes to occur to
the organism.
Fossil Wasp from Eocene lake beds at Florissant
Fossil Beds National Monument.
(photo by Bud Wobus).