Transcript 5-2 The Fossil Record

5-2 The Fossil Record
http://www.kpbsd.k12.ak.us/chapman/demers/images/collage2.JPG
What is a fossil?
• Some of the most important clues to
Earth’s past are fossils.
• A fossil is the preserved remains or traces
of an organism that lived in the past.
• Most fossils form when organisms that die
become buried in sediments (particles of
soil and rock).
Why are fossils important?
• It enabled scientists to see occurrence of
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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
It shows evidence of continental drift – the
belief that the continents were once one large
landmass
Plummer et al 2003
Fossilization
• Hard parts of organisms are more likely to be
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preserve 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
• Petrified Fossils – remains that become buried in
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sediments and actually changed to rock.
Mold – a hollow space in sediment in the shape
of an organism or part of an organism
Cast – copy of the shape of the organism that
made the mold
Preserved Remains – entire organisms kept
intact in ice, tar, or amber
Traces – other evidence that an organism
existed, ex. tracks, trails, footprints
Preserved Remains
Petrified Fossils
http://www.fp.sfasu.edu/geolog
y/GeologyTutorial/Fossils/CARB
ONization01.JPG
http://www.fossilmall.com/Ston
erelic/amber/a25/bazaar_hemi
pteran_a25.htm
Impression - Cast and Mold
http://gpc.edu/~pgore/myphotos/fossils/cast
&mold.jpg
Petrified wood
http://www.clas.ufl.edu/users/pciesiel/gly3
603c/wood1.jpg
Trace fossil
http://www.dinosaursrock.com/Steve
DiloposaurusFootPrint.jpg
Age on Earth
• Scientists can determine a fossils age in
two ways:
• relative dating: used to determine which
of two rocks is older (layers at the top of
the rock are younger than layers at the
bottom)
• Absolute dating : used to determine the
actual age of fossils
Fossil Record
• The millions of fossils that scientists have
collected
• A species is extinct if no members of that
species are still alive
Relative Dating Using Fossils
http://www.carleton.ca/~tpatters/teaching/climatechange/rocks/rocks11.gif
Geologic Time Scale
• A calendar of Earth’s history that spans over 4.6
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billion years.
Scientists have divided this large time period
into smaller units called eras and periods.
The largest span in the calendar is the
Precambrian Era.
Very few fossils are found from the Precambrian
Era
Plummer et al 2003
Also called Hadean
http://books.nap.edu/html/creationism/evidence.html
Theories of Evolution
• Gradualism – evolution occurs slowly but
steadily
• Punctuated equilibria – species evolve
during short periods of rapid change