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Fossils: Our Keys to the Past and Evidence
of Evolution
By: Shannon Reardon
Adam Bouchard
and Kristan Brodie
What is a fossil?
• A fossil is remains of ancient life
• Fossil is derived from the Latin term
fossilis - meaning any object extracted
from the ground including minerals and
archeological artifacts
paleo ology (the study
• In the 18th century paleontology
of ancient life) was created
= old or ancient
= study of
Why are fossils important?
• It enabled scientists to see occurrence of
extinction in different species
• It gave Darwin evidence that earth is older than
previously believed and that very slow changes
over a long period of time can add up to
substantial changes in organisms
• Can be used to correlate and match up rock
units from different places giving relative ages
• It shows evidence of continental drift – the
theory that continents were once one large
Plummer et al 2003
• Hard parts of organisms are more likely to be
preserved than soft parts.
• Soft parts are likely to decay or be consumed by
other organisms
• Because of this soft bodied creatures such as
jellyfish may not be fossilized either
• Buried organisms are more likely to be fossilized
because it minimizes the decay, consumption,
and destruction of the remains
Types of Fossils
• Unaltered remains – original material of the
organism has not been changed to another
• Altered remains – original material has
undergone permineralization, recrystalization,
replacement, carbonization
• Impressions – organisms leave an imprint in
sediment, can form casts and molds
• Traces – other evidence that an organism
existed, ex. tracks, trails, footprints
Unaltered Parts
Altered remains
Carbonization of a leaf
Impression - Cast and Mold
Permineralization –
petrified wood
Trace fossil
Radioactive Dating and
Geologic Time Scale
By Adam Bouchard
Age on Earth
• EVIDENCE suggests age of the Earth is
about 4.6 to 4.7 billion years old
• Evidence is gathered from radioactive
dating of rocks from the earth, moon and
• Relative age : places rock units or
geologic events in sequential order
• Absolute age : numerical or chronological
age of a rock or geologic event
Radioactive Dating Definitions
• Radioactive isotope - an atomic form of a
chemical element that is unstable
• Radioactive decay - the spontaneous nuclear
disintegration of certain isotopes
• Radioactive dating – a way of determining the
age of rocks and fossils on a scale of absolute
time. It is based on the half-life of radioactive
• Half-life – the time it takes for ½ the atoms of
the radioactive parent to decay to atoms of the
daughter element
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