Fossils: Our Keys to the Past and Evidence of Evolution

By: Shannon Reardon Adam Bouchardand Kristan Brodie

http://www.kpbsd.k12.ak.us/chapman/demers/images/collage2.JPG

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

• In the 18th century paleontology (the study of ancient life) was created

= old or ancient = study of

paleopaleo ologyology

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 landmass

Plummer et al 2003

Fossilization

• 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

izatioizationn

= TO MAKE

BURIED IN SEDIMENT OR SOIL

Types of Fossils

• Unaltered remains – original material of the organism has not been changed to another substance

• 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

http://www.studyworksonline.com/cda/image/preview/0,1127,1309,00.jpg

http://gpc.edu/~pgore/myphotos/fossils/cast&mold.jpg

http://www.fp.sfasu.edu/geology/GeologyTutorial/Fossils/CARBONization01.JPG

Trace fossil

http://www.dinosaursrock.com/SteveDiloposaurusFootPrint.jpg

Permineralization – petrified wood

http://www.clas.ufl.edu/users/pciesiel/gly3603c/wood1.jpg

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 meteorites

• 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 isotopes

• 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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